Paleoclimatic records from the Bay of Bengal are rare. We reconstruct the sea-surface temperature... more Paleoclimatic records from the Bay of Bengal are rare. We reconstruct the sea-surface temperature (SST) and salinity from paired δ 18 O and Mg/Ca measurements in planktonic foraminifera Globigerinoides ruber from the western Bay of Bengal core VM29-19. Our data suggest that SST and seawater δ 18 O (δ 18 O sw ) were ~3°C colder and ~0.6‰ depleted, respectively, during the Last Glacial Maximum (LGM) compared to the early Holocene. The most enriched δ 18 O sw values were found between 18.2 and 15.6 ka interval. Depleted LGM δ 18 O sw values suggest a wet climate which freshened the Bay of Bengal sea surface. Our data further indicate that the monsoon was stronger in the Bølling/Allerød and weaker in the Younger Dryas periods. The most depleted early Holocene δ 18 O sw values suggest that the monsoon was stronger and wetter resulting in a humid climate. After ~5 ka the Indian summer monsoon weakened significantly, indicating less dilution of the sea surface by the Ganges-Brahmaputra-Meghna outflow and/or less direct rainfall. We hypothesize that the prevailing late Holocene dry climate may have caused the diminishment and subsequent abandonment of the settlements of the great Indus Valley Civilizations. Our Bay of Bengal climate records are consistent with those from the Andaman Sea, corroborating broad regional changes in the Indian summer monsoon during the last 25 ka. The general pattern and timing of monsoon variability in the Bay of Bengal and Andaman Sea seems to parallel the Arabian Sea, Africa, and Asian ice cores and speleothem records suggesting that a common tropical forcing may have induced these abrupt climate changes.
Proceedings of the Nova Scotian Institute of Science, 2024
After two decades of planning and negotiations, the United Nations (UN) announced the passage of ... more After two decades of planning and negotiations, the United Nations (UN) announced the passage of the High Seas Treaty on March 4, 2023. The Treaty aims to protect biodiversity in international waters, and the UN believes it will enable the enhancement and management of the ocean’s resilience by allowing for the creation of marine protected areas (i.e., safe havens for fish, plants, and other vulnerable species) and the so-called “area-based management tools.” Its broad intent is to support billions of people worldwide who rely on the oceans for basic needs (Kim 2023). It has been demonstrated that maintaining biodiversity is one of the key pillars to maintaining oceans’ trophic levels (ocean food chain); by extension, it implies a sustainable human food supply. However, the task of selecting appropriate measures of biodiversity that have utility for international ocean management issues will require further study. For example, Harris (2007) notes that “what we now regard as the normal state of the oceans has been severely perturbed by the removal of top predators.” It is also equally important to assess modification caused by unintended introduction of alien species, open ocean aquaculture, range of pharmaceuticals, anthropogenic chemicals, etc.
Sites of ice-stream discharge to the continental slope build trough-mouth fans from glacigenic de... more Sites of ice-stream discharge to the continental slope build trough-mouth fans from glacigenic debris flows (GDFs), subglacial meltwater flows, and suspended sediment. Thus, past ice configurations may be interpreted from the sedimentological record. This study links the records in cores, high-resolution seismic profiles, and multibeam swath bathymetry of Hatton Slope and Fan to the changing glaciological history in Hudson Strait, one of the largest ice streams of the late Pleistocene Laurentide Ice Sheet. 14 C-AMS dates, X-ray fluorescence geochemical profiles, and oxygen isotopes in sixteen cores document sediment supply during the last glacial cycle, and earlier history is interpreted from seismic data. The Frobisher Bay slope sector has a long record of GDF deposits from severe glacial periods between MIS 6 and 22, with little impact of meltwater discharge. Masstransport events and aggrading gravel-floored valleys dominate the northern Hatton slope sector. The central slope sector shows the greatest shelf
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Late Pleistocene Labrador Sea depositional systems developed in front of ice streams and glacier ... more Late Pleistocene Labrador Sea depositional systems developed in front of ice streams and glacier outlets from the Laurentide Ice Sheet (LIS) are documented by Huntec and 3.5 kHz seismic profiles and piston cores. Due to efficient grinding by the LIS, massive amounts of fine-grained sediments and meltwater in addition to the icebergs linked to the Heinrich events (H events) of the last glaciation were delivered to the neighboring Labrador Sea. The position of the Hudson Strait ice stream during the periodic expansion and contraction on the Labrador margin allowed fine-grained sediments and meltwater direct delivery on the lower shelf and upper slope. These discharges were then transported southward by the Labrador Current and western boundary current. In contrast to the lower shelf and upper slope, sediments delivered on the mid to the lower Labrador Slope were transported by the Northwest Atlantic Mid-Ocean Channel to distal sites. The nepheloid flow layer at or near the sea bottom ...
ABSTRACT Further study of fifty cores from the Labrador Sea reveals the presence of eight Heinric... more ABSTRACT Further study of fifty cores from the Labrador Sea reveals the presence of eight Heinrich events, i.e., H0-H6, including H5a. Heinrich layers in the Labrador Sea are identified by their high detrital carbonate concentration, increased coarse-fraction content, and lighter YO18O values in Neogloboquadrina pachyderma (sinistral). Heinrich layers in ice-proximal regions of the Labrador Sea are dominated by nepheloid-flow deposits that are recognized in X-radiographs as thin graded mud layers with floating coarser grains of ice-rafted detritus (IRD) as opposed to those in the North Atlantic which consist of pelagic sediments rich in IRD. The concentration of IRD within Heinrich layers H1 and H2 in the upper slope of the northwestern Labrador Sea cores shows a double peak dominated by detrital carbonate grains, whereas the lower-slope and deep Labrador-basin cores show a single peak. These findings are in contrast with North Atlantic Heinrich layers that are characterized by a double peak of IRD; a peak of quartz and volcanic grains followed by a carbonate peak. There are light dO18 peaks observed immediately prior to H2 and H1 which are neither associated with an increase in IRD nor with the concentration of detrital carbonate. The distribution and thickness of Heinrich layers suggest that iceberg discharge during different Heinrich events in the Labrador Sea followed different drift routes. Heinrich-like event H0 is present only in the upper slope cores of the northwestern Labrador Sea close to Hudson Strait but absent in the lower slope and deep-basin cores. During or prior to H0, the Laurentide Ice Sheet may have retreated to the inner shelf (or more landward), hence the glaciomarine sediments delivered to the inner shelf and icebergs were transported by the already established Labrador Current. On the other hand, during the deposition of earlier Heinrich events, iceberg discharge was so massive that it overwhelmed the Labrador Current and swamped the open Labrador Sea with icebergs. A narrow light dO18-Npl peak at the end of H2 and H4 preceded by heavier values during these events in all proximal cores suggests that the iceberg supply was predominant over meltwater discharge. This might indicate that ocean surface temperatures were too low to allow major iceberg melting toward the end of those Heinrich events when warming started. It is proposed that H3 and H5a in the Labrador Sea, on the other hand, may have been associated with major melt-water discharge.
Ten piston cores and a 25 m long giant piston core from the ice-proximal region off Hudson Strait... more Ten piston cores and a 25 m long giant piston core from the ice-proximal region off Hudson Strait contain Heinrich layers 1 and 2, identified by their sedimentary structure and high detrital carbonate content. Both layers are unusually thick on the upper Labrador slope (3.8^2.1 m) and on the lower slope and rise (1.5^1.0 m). Heinrich layers 1 and 2 can be subdivided into three units. Unit A is restricted to the upper slope and overlies hemipelagic sediment with a gradational boundary. It is 6 1 m thick, dark black to dark gray in color, and made up of coarse ice-rafted sand and granules dispersed in hemipelagic mud with a few faint laminations towards the top. The overlying unit B is up to 3.35 m thick and consists of two facies: (i) centimeter-thick, graded, carbonate-rich mud layers containing dispersed coarser grains in the mud, interpreted as nepheloid-flow deposits with coarse ice-rafted debris, and (ii) carbonate-rich, finely laminated mud layers, which alternate with millimeter-thick laminae of ice-rafted debris. Unit C, up to 0.90 m thick, is devoid of sedimentary structures, and consists of hemipelagic sediment with dispersed dropstones that increase in abundance towards the top of the unit. Data suggest the following sequence of processes could have occurred during the deposition of Heinrich layers in ice-proximal sites. As the Laurentide Ice Sheet grew, it extended through the Hudson Strait ice stream outlet to a floating ice margin near the shelf edge and perhaps beyond to the upper slope, and deposited unit A by releasing dropstones from the basal debris-rich layer. Unit B is interpreted to be the deposits of the combined processes of nepheloid-layer flow, low-density turbidity currents, and massive ice-rafting. Maximum carbonate content (s 50%), the lightest N 18 O values in very sparse planktonic foraminifera, and low magnetic susceptibility are characteristic of unit B. Unit C is inferred to represent the time of waning supply of fines as nepheloid-flow deposition ceased, while the relative concentration of dropstones increased as a result of continuing intense ice-rafting. Due to the reduction of fine-grained sediment supply, the carbonate concentration decreased to the Labrador Sea background level. This finding was further supported by the appearance of darker-colored sediments and heavier N 18 O values in Neogloboquadrina pachyderma (s) which indicates the reduction of meltwater discharge towards the end of a Heinrich event.
An additional Heinrich ice-rafting event is identified between Heinrich events 5 and 6 in eight c... more An additional Heinrich ice-rafting event is identified between Heinrich events 5 and 6 in eight cores from the Labrador Sea and the northwest Atlantic Ocean. It is characterized by sediment rich in detrital carbonate (40% CaCO 3) with high concentration of floating dropstones, high coarse-fraction (% > 150 mm) content, and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment. It also shows lighter d 18 O Npl values, indicating freshening due to iceberg rafting and/or meltwater discharge. This event is correlated with Dansgaard-Oeschger event 14 and interpreted as an additional Heinrich event, H5a. The thickness of H5a in the Labrador Sea reaches up to 220 cm. This additional Heinrich event has also been reported in cores PS2644 and SO82-5 from the northern North Atlantic. With the recognition of H5a the temporal spacing between Heinrich events 1 to 6 becomes more uniform ($7 ka).
(2) , Jens Schröter (3) , Victor Zlotnicki (4) , Peter Bender (5) , Alexander Braun (6) , Anny Ca... more (2) , Jens Schröter (3) , Victor Zlotnicki (4) , Peter Bender (5) , Alexander Braun (6) , Anny Cazenave (7) , Don Chamber (8) , Jianbin Duan (1) , William Emery (9) , Georgia Fotopoulos (6) , Viktor Gouretski (10) , Richard Gross (4) , Thomas Gruber (11) , Junyi Guo (1) , Guoqi Han (12) , Chris Hughes (13) , Masayoshi Ishii (14) , Steven Jayne (15) , Johnny Johannesen (16) , Per Knudsen (17) , Chung-Yen Kuo (18) , Eric Leuliette (19) , Sydney Levitus (20) , Nikolai Maximenko (21) , Laury Miller (19) , James Morison (22) , Harunur Rashid (23) , John Ries (24) , Markus Rothacher (25) , Reiner Rummel (11) , Kazuo Shibuya (26) , Michael Sideris (27) , Y. Tony Song (4) , Detlef Stammer (28) , Maik Thomas (29) , Josh Willis (4) , Philip Woodworth (13)
The SE Grand Banks Slope is unusual on the glaciated eastern Canadian margin in that it was remot... more The SE Grand Banks Slope is unusual on the glaciated eastern Canadian margin in that it was remote from ice stream and glacial ice of the Laurentide Ice Sheet (LIS). It thus allows an analysis of the role of contour currents and landslides in sculpting the continental margin, processes that are largely masked where downslope proglacial sediment supply dominated. Detailed oxygen isotope, geotechnical, pXRF, and bulk sediment geochemical analyses were made on seven piston cores and were placed in context using multi-beam bathymetry and high-resolution seismic reflection profiles. Cores have a record of sedimentation back to MIS6 preserved in autochthonous sediment and slide blocks, contourites and mass-transport deposits (MTDs). Detrital-carbonaterich Heinrich layers (H) are present throughout the succession, but red mud layers of glacial meltwater origin from ice-streams in the SE sector of the LIS are identified only during MIS2 and late MIS3. Both layers allowed high-resolution correlation between cores. Sediments on the upper slope above H2 are condensed and the section above H1 is < 50 cm thick, indicating that the powerful Labrador Current winnowed the section above H2. In contrast to the upper slope, approximately 3 to 5 m sediments were recorded in the mid-slope above H2 suggesting that the Labrador Current was weaker. Regional stratigraphic variations compared to Flemish Pass and Orphan Basin to the north suggest that NE Newfoundland sources of sediment played an important role and may have been previously underestimated. This study demonstrates that across-margin thickness variations reflect the character and distribution of the Labrador Current sediment transport system through time. Five horizons with MTDs with headscarps generally up to 25 m high are recognized in the upper 50-70 m. Thick MTDs are blocky in cores and in their seismic and bathymetric expression resemble spreads, with local thin mud clast conglomerates that ran out as debris flows over the contemporaneous seabed. Geotechnical data suggest that the seabed is stable under static conditions, although there is geological evidence for fluid escape and geotechnical evidence for underconsolidation. Weak layers along which failure took place are found somewhere around H3-H4 and at or near the top of H5 and MIS6. The low plasticity and liquid limit of the H layers make these layers susceptible to failure during cyclic loading. Episodic earthquakes are the most likely cause of failure. meltwater. Two large ice-streams, namely the Hudson Strait (Rashid and Piper, 2007) and the Laurentian Channel ice-streams (Piper et al., 2007), delivered sediment to the southward flowing Labrador Current and its southwestward continuation. There are several smaller icestreams on the Labrador, NE Newfoundland, and Scotian margins, but no ice-streams have been recognized on the Grand Banks between Trinity Trough and Haddock Channel (Fig. 1), even though an ice-sheet was centered on Newfoundland (Shaw et al., 2006; their Fig. 8). As a
An additional Heinrich ice-rafting event is identified between Heinrich events 5 and 6 in eight c... more An additional Heinrich ice-rafting event is identified between Heinrich events 5 and 6 in eight cores from the Labrador Sea and the northwest Atlantic Ocean. It is characterized by sediment rich in detrital carbonate (40% CaCO3) with high concentration of floating dropstones, high coarse-fraction (% > 150 µm) content, and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment. It also shows lighter d18ONpl values, indicating freshening due to iceberg rafting and/or meltwater discharge. This event is correlated with Dansgaard-Oeschger event 14 and interpreted as an additional Heinrich event, H5a. The thickness of H5a in the Labrador Sea reaches up to 220 cm. This additional Heinrich event has also been reported in cores PS2644 and SO82-5 from the northern North Atlantic. With the recognition of H5a the temporal spacing between Heinrich events 1 to 6 becomes more uniform (~7 ka).
Climate data over the past two decades show that abrupt millennial-scale climate changes brought ... more Climate data over the past two decades show that abrupt millennial-scale climate changes brought dramatic changes in temperature and greenhouse gases during the last glacial–interglacial cycle. However, the millennial-scale changes in the tropics were associated with both dramatic weakening and strengthening of the hydrological cycle. The early Holocene was warmer and wetter than the present climate, resulting in over-spilling of North African lakes and overflow of rivers on the Indian subcontinent. In contrast, the late Holocene, accompanied by a dry and windy climate, is thought to be responsible for desertification of North Africa and reduced outflow of Indian subcontinent rivers. The prevalence of this dry climate during the late Holocene is inferred to have led to the decline or demise of many ancient civilizations.
The role of Labrador Current (LC) in providing freshwater to the North Atlantic and hence modulat... more The role of Labrador Current (LC) in providing freshwater to the North Atlantic and hence modulating the Atlantic meridional overturning circulation (AMOC) has been debated with very few data. This study provides the first data on the relative speed of the LC for the past 9.2 ka using mean size of the sortable silt of sediments as a proxy from a mid-shelf basin in the western Labrador Sea. LC speed progressively intensified from 9.2-5 ka, during which two meltwater events had minor influence. The LC was fastest between 5 ka and 3.1 ka and gradually weakened after 3.1 ka. The mean size of the sortable silt data shows overall covariations with similar existing data from deep-water areas of the greater North Atlantic, suggesting an overarching link that modulates changes in both the near-surface and deep North Atlantic. A dynamical link between the LC and AMOC vigor is hypothesized in which high meltwater discharge in the Labrador Sea oriented the subpolar gyre (SPG) more North-South (meridional), weakening the SPG, and thus decelerating the upper limb of the AMOC. Conversely, reduction in LC transport during the late Holocene, due to the greater export of sea ice, oriented the SPG more East-West.
... d'Etudes en Géophysique et Océanographie Spatiales, LEGOS-CNES, Observatoire Midi-Pyréné... more ... d'Etudes en Géophysique et Océanographie Spatiales, LEGOS-CNES, Observatoire Midi-Pyrénées, Toulouse, France, [email protected] ... Physical Oceanography Dept., Woods Hole Oceanographic Institution, Woods Hole, MA, USA, [email protected] Chung-yen Kuo ...
The presence of Heinrich layer 3 (HL-3) in the northwest Labrador Sea has been debated in the lit... more The presence of Heinrich layer 3 (HL-3) in the northwest Labrador Sea has been debated in the literature. Calypso giant piston core MD99-2233, five new standard piston cores, and re-interpretation of 34 cores from previous cruises confirm the presence of HL-3 in the Labrador Sea. It is identified by high total carbonate concentration (up to 45%), an increase in coarse fraction content, and lighter N 18 O values in polar species planktonic foraminifer Neogloboquadrina pachyderma (left-coiling) as low as 3.1x. The age of HL-3 of V27 ka was bracketed in the various cores by about 50 14 C-accelerator mass spectrometer dates. Where it is present in ice-proximal regions, it consists of nepheloid-flow deposits at the base and mud turbidites at the top. The thickness of HL-3 varies between 4.8 m (proximal to Hudson Strait) and 0.9 m (distal), decreasing rapidly seaward. On the upper continental slope, HL-3 was too deeply buried to be sampled. Elsewhere, HL-3 is absent in some cores, probably due to slumping or erosion associated with sandy turbidity currents or debris flows.
Logging data are measurements of physical properties of the formation surrounding a borehole, acq... more Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Paleoclimatic records from the Bay of Bengal are rare. We reconstruct the sea-surface temperature... more Paleoclimatic records from the Bay of Bengal are rare. We reconstruct the sea-surface temperature (SST) and salinity from paired δ 18 O and Mg/Ca measurements in planktonic foraminifera Globigerinoides ruber from the western Bay of Bengal core VM29-19. Our data suggest that SST and seawater δ 18 O (δ 18 O sw ) were ~3°C colder and ~0.6‰ depleted, respectively, during the Last Glacial Maximum (LGM) compared to the early Holocene. The most enriched δ 18 O sw values were found between 18.2 and 15.6 ka interval. Depleted LGM δ 18 O sw values suggest a wet climate which freshened the Bay of Bengal sea surface. Our data further indicate that the monsoon was stronger in the Bølling/Allerød and weaker in the Younger Dryas periods. The most depleted early Holocene δ 18 O sw values suggest that the monsoon was stronger and wetter resulting in a humid climate. After ~5 ka the Indian summer monsoon weakened significantly, indicating less dilution of the sea surface by the Ganges-Brahmaputra-Meghna outflow and/or less direct rainfall. We hypothesize that the prevailing late Holocene dry climate may have caused the diminishment and subsequent abandonment of the settlements of the great Indus Valley Civilizations. Our Bay of Bengal climate records are consistent with those from the Andaman Sea, corroborating broad regional changes in the Indian summer monsoon during the last 25 ka. The general pattern and timing of monsoon variability in the Bay of Bengal and Andaman Sea seems to parallel the Arabian Sea, Africa, and Asian ice cores and speleothem records suggesting that a common tropical forcing may have induced these abrupt climate changes.
Proceedings of the Nova Scotian Institute of Science, 2024
After two decades of planning and negotiations, the United Nations (UN) announced the passage of ... more After two decades of planning and negotiations, the United Nations (UN) announced the passage of the High Seas Treaty on March 4, 2023. The Treaty aims to protect biodiversity in international waters, and the UN believes it will enable the enhancement and management of the ocean’s resilience by allowing for the creation of marine protected areas (i.e., safe havens for fish, plants, and other vulnerable species) and the so-called “area-based management tools.” Its broad intent is to support billions of people worldwide who rely on the oceans for basic needs (Kim 2023). It has been demonstrated that maintaining biodiversity is one of the key pillars to maintaining oceans’ trophic levels (ocean food chain); by extension, it implies a sustainable human food supply. However, the task of selecting appropriate measures of biodiversity that have utility for international ocean management issues will require further study. For example, Harris (2007) notes that “what we now regard as the normal state of the oceans has been severely perturbed by the removal of top predators.” It is also equally important to assess modification caused by unintended introduction of alien species, open ocean aquaculture, range of pharmaceuticals, anthropogenic chemicals, etc.
Sites of ice-stream discharge to the continental slope build trough-mouth fans from glacigenic de... more Sites of ice-stream discharge to the continental slope build trough-mouth fans from glacigenic debris flows (GDFs), subglacial meltwater flows, and suspended sediment. Thus, past ice configurations may be interpreted from the sedimentological record. This study links the records in cores, high-resolution seismic profiles, and multibeam swath bathymetry of Hatton Slope and Fan to the changing glaciological history in Hudson Strait, one of the largest ice streams of the late Pleistocene Laurentide Ice Sheet. 14 C-AMS dates, X-ray fluorescence geochemical profiles, and oxygen isotopes in sixteen cores document sediment supply during the last glacial cycle, and earlier history is interpreted from seismic data. The Frobisher Bay slope sector has a long record of GDF deposits from severe glacial periods between MIS 6 and 22, with little impact of meltwater discharge. Masstransport events and aggrading gravel-floored valleys dominate the northern Hatton slope sector. The central slope sector shows the greatest shelf
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Late Pleistocene Labrador Sea depositional systems developed in front of ice streams and glacier ... more Late Pleistocene Labrador Sea depositional systems developed in front of ice streams and glacier outlets from the Laurentide Ice Sheet (LIS) are documented by Huntec and 3.5 kHz seismic profiles and piston cores. Due to efficient grinding by the LIS, massive amounts of fine-grained sediments and meltwater in addition to the icebergs linked to the Heinrich events (H events) of the last glaciation were delivered to the neighboring Labrador Sea. The position of the Hudson Strait ice stream during the periodic expansion and contraction on the Labrador margin allowed fine-grained sediments and meltwater direct delivery on the lower shelf and upper slope. These discharges were then transported southward by the Labrador Current and western boundary current. In contrast to the lower shelf and upper slope, sediments delivered on the mid to the lower Labrador Slope were transported by the Northwest Atlantic Mid-Ocean Channel to distal sites. The nepheloid flow layer at or near the sea bottom ...
ABSTRACT Further study of fifty cores from the Labrador Sea reveals the presence of eight Heinric... more ABSTRACT Further study of fifty cores from the Labrador Sea reveals the presence of eight Heinrich events, i.e., H0-H6, including H5a. Heinrich layers in the Labrador Sea are identified by their high detrital carbonate concentration, increased coarse-fraction content, and lighter YO18O values in Neogloboquadrina pachyderma (sinistral). Heinrich layers in ice-proximal regions of the Labrador Sea are dominated by nepheloid-flow deposits that are recognized in X-radiographs as thin graded mud layers with floating coarser grains of ice-rafted detritus (IRD) as opposed to those in the North Atlantic which consist of pelagic sediments rich in IRD. The concentration of IRD within Heinrich layers H1 and H2 in the upper slope of the northwestern Labrador Sea cores shows a double peak dominated by detrital carbonate grains, whereas the lower-slope and deep Labrador-basin cores show a single peak. These findings are in contrast with North Atlantic Heinrich layers that are characterized by a double peak of IRD; a peak of quartz and volcanic grains followed by a carbonate peak. There are light dO18 peaks observed immediately prior to H2 and H1 which are neither associated with an increase in IRD nor with the concentration of detrital carbonate. The distribution and thickness of Heinrich layers suggest that iceberg discharge during different Heinrich events in the Labrador Sea followed different drift routes. Heinrich-like event H0 is present only in the upper slope cores of the northwestern Labrador Sea close to Hudson Strait but absent in the lower slope and deep-basin cores. During or prior to H0, the Laurentide Ice Sheet may have retreated to the inner shelf (or more landward), hence the glaciomarine sediments delivered to the inner shelf and icebergs were transported by the already established Labrador Current. On the other hand, during the deposition of earlier Heinrich events, iceberg discharge was so massive that it overwhelmed the Labrador Current and swamped the open Labrador Sea with icebergs. A narrow light dO18-Npl peak at the end of H2 and H4 preceded by heavier values during these events in all proximal cores suggests that the iceberg supply was predominant over meltwater discharge. This might indicate that ocean surface temperatures were too low to allow major iceberg melting toward the end of those Heinrich events when warming started. It is proposed that H3 and H5a in the Labrador Sea, on the other hand, may have been associated with major melt-water discharge.
Ten piston cores and a 25 m long giant piston core from the ice-proximal region off Hudson Strait... more Ten piston cores and a 25 m long giant piston core from the ice-proximal region off Hudson Strait contain Heinrich layers 1 and 2, identified by their sedimentary structure and high detrital carbonate content. Both layers are unusually thick on the upper Labrador slope (3.8^2.1 m) and on the lower slope and rise (1.5^1.0 m). Heinrich layers 1 and 2 can be subdivided into three units. Unit A is restricted to the upper slope and overlies hemipelagic sediment with a gradational boundary. It is 6 1 m thick, dark black to dark gray in color, and made up of coarse ice-rafted sand and granules dispersed in hemipelagic mud with a few faint laminations towards the top. The overlying unit B is up to 3.35 m thick and consists of two facies: (i) centimeter-thick, graded, carbonate-rich mud layers containing dispersed coarser grains in the mud, interpreted as nepheloid-flow deposits with coarse ice-rafted debris, and (ii) carbonate-rich, finely laminated mud layers, which alternate with millimeter-thick laminae of ice-rafted debris. Unit C, up to 0.90 m thick, is devoid of sedimentary structures, and consists of hemipelagic sediment with dispersed dropstones that increase in abundance towards the top of the unit. Data suggest the following sequence of processes could have occurred during the deposition of Heinrich layers in ice-proximal sites. As the Laurentide Ice Sheet grew, it extended through the Hudson Strait ice stream outlet to a floating ice margin near the shelf edge and perhaps beyond to the upper slope, and deposited unit A by releasing dropstones from the basal debris-rich layer. Unit B is interpreted to be the deposits of the combined processes of nepheloid-layer flow, low-density turbidity currents, and massive ice-rafting. Maximum carbonate content (s 50%), the lightest N 18 O values in very sparse planktonic foraminifera, and low magnetic susceptibility are characteristic of unit B. Unit C is inferred to represent the time of waning supply of fines as nepheloid-flow deposition ceased, while the relative concentration of dropstones increased as a result of continuing intense ice-rafting. Due to the reduction of fine-grained sediment supply, the carbonate concentration decreased to the Labrador Sea background level. This finding was further supported by the appearance of darker-colored sediments and heavier N 18 O values in Neogloboquadrina pachyderma (s) which indicates the reduction of meltwater discharge towards the end of a Heinrich event.
An additional Heinrich ice-rafting event is identified between Heinrich events 5 and 6 in eight c... more An additional Heinrich ice-rafting event is identified between Heinrich events 5 and 6 in eight cores from the Labrador Sea and the northwest Atlantic Ocean. It is characterized by sediment rich in detrital carbonate (40% CaCO 3) with high concentration of floating dropstones, high coarse-fraction (% > 150 mm) content, and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment. It also shows lighter d 18 O Npl values, indicating freshening due to iceberg rafting and/or meltwater discharge. This event is correlated with Dansgaard-Oeschger event 14 and interpreted as an additional Heinrich event, H5a. The thickness of H5a in the Labrador Sea reaches up to 220 cm. This additional Heinrich event has also been reported in cores PS2644 and SO82-5 from the northern North Atlantic. With the recognition of H5a the temporal spacing between Heinrich events 1 to 6 becomes more uniform ($7 ka).
(2) , Jens Schröter (3) , Victor Zlotnicki (4) , Peter Bender (5) , Alexander Braun (6) , Anny Ca... more (2) , Jens Schröter (3) , Victor Zlotnicki (4) , Peter Bender (5) , Alexander Braun (6) , Anny Cazenave (7) , Don Chamber (8) , Jianbin Duan (1) , William Emery (9) , Georgia Fotopoulos (6) , Viktor Gouretski (10) , Richard Gross (4) , Thomas Gruber (11) , Junyi Guo (1) , Guoqi Han (12) , Chris Hughes (13) , Masayoshi Ishii (14) , Steven Jayne (15) , Johnny Johannesen (16) , Per Knudsen (17) , Chung-Yen Kuo (18) , Eric Leuliette (19) , Sydney Levitus (20) , Nikolai Maximenko (21) , Laury Miller (19) , James Morison (22) , Harunur Rashid (23) , John Ries (24) , Markus Rothacher (25) , Reiner Rummel (11) , Kazuo Shibuya (26) , Michael Sideris (27) , Y. Tony Song (4) , Detlef Stammer (28) , Maik Thomas (29) , Josh Willis (4) , Philip Woodworth (13)
The SE Grand Banks Slope is unusual on the glaciated eastern Canadian margin in that it was remot... more The SE Grand Banks Slope is unusual on the glaciated eastern Canadian margin in that it was remote from ice stream and glacial ice of the Laurentide Ice Sheet (LIS). It thus allows an analysis of the role of contour currents and landslides in sculpting the continental margin, processes that are largely masked where downslope proglacial sediment supply dominated. Detailed oxygen isotope, geotechnical, pXRF, and bulk sediment geochemical analyses were made on seven piston cores and were placed in context using multi-beam bathymetry and high-resolution seismic reflection profiles. Cores have a record of sedimentation back to MIS6 preserved in autochthonous sediment and slide blocks, contourites and mass-transport deposits (MTDs). Detrital-carbonaterich Heinrich layers (H) are present throughout the succession, but red mud layers of glacial meltwater origin from ice-streams in the SE sector of the LIS are identified only during MIS2 and late MIS3. Both layers allowed high-resolution correlation between cores. Sediments on the upper slope above H2 are condensed and the section above H1 is < 50 cm thick, indicating that the powerful Labrador Current winnowed the section above H2. In contrast to the upper slope, approximately 3 to 5 m sediments were recorded in the mid-slope above H2 suggesting that the Labrador Current was weaker. Regional stratigraphic variations compared to Flemish Pass and Orphan Basin to the north suggest that NE Newfoundland sources of sediment played an important role and may have been previously underestimated. This study demonstrates that across-margin thickness variations reflect the character and distribution of the Labrador Current sediment transport system through time. Five horizons with MTDs with headscarps generally up to 25 m high are recognized in the upper 50-70 m. Thick MTDs are blocky in cores and in their seismic and bathymetric expression resemble spreads, with local thin mud clast conglomerates that ran out as debris flows over the contemporaneous seabed. Geotechnical data suggest that the seabed is stable under static conditions, although there is geological evidence for fluid escape and geotechnical evidence for underconsolidation. Weak layers along which failure took place are found somewhere around H3-H4 and at or near the top of H5 and MIS6. The low plasticity and liquid limit of the H layers make these layers susceptible to failure during cyclic loading. Episodic earthquakes are the most likely cause of failure. meltwater. Two large ice-streams, namely the Hudson Strait (Rashid and Piper, 2007) and the Laurentian Channel ice-streams (Piper et al., 2007), delivered sediment to the southward flowing Labrador Current and its southwestward continuation. There are several smaller icestreams on the Labrador, NE Newfoundland, and Scotian margins, but no ice-streams have been recognized on the Grand Banks between Trinity Trough and Haddock Channel (Fig. 1), even though an ice-sheet was centered on Newfoundland (Shaw et al., 2006; their Fig. 8). As a
An additional Heinrich ice-rafting event is identified between Heinrich events 5 and 6 in eight c... more An additional Heinrich ice-rafting event is identified between Heinrich events 5 and 6 in eight cores from the Labrador Sea and the northwest Atlantic Ocean. It is characterized by sediment rich in detrital carbonate (40% CaCO3) with high concentration of floating dropstones, high coarse-fraction (% > 150 µm) content, and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment. It also shows lighter d18ONpl values, indicating freshening due to iceberg rafting and/or meltwater discharge. This event is correlated with Dansgaard-Oeschger event 14 and interpreted as an additional Heinrich event, H5a. The thickness of H5a in the Labrador Sea reaches up to 220 cm. This additional Heinrich event has also been reported in cores PS2644 and SO82-5 from the northern North Atlantic. With the recognition of H5a the temporal spacing between Heinrich events 1 to 6 becomes more uniform (~7 ka).
Climate data over the past two decades show that abrupt millennial-scale climate changes brought ... more Climate data over the past two decades show that abrupt millennial-scale climate changes brought dramatic changes in temperature and greenhouse gases during the last glacial–interglacial cycle. However, the millennial-scale changes in the tropics were associated with both dramatic weakening and strengthening of the hydrological cycle. The early Holocene was warmer and wetter than the present climate, resulting in over-spilling of North African lakes and overflow of rivers on the Indian subcontinent. In contrast, the late Holocene, accompanied by a dry and windy climate, is thought to be responsible for desertification of North Africa and reduced outflow of Indian subcontinent rivers. The prevalence of this dry climate during the late Holocene is inferred to have led to the decline or demise of many ancient civilizations.
The role of Labrador Current (LC) in providing freshwater to the North Atlantic and hence modulat... more The role of Labrador Current (LC) in providing freshwater to the North Atlantic and hence modulating the Atlantic meridional overturning circulation (AMOC) has been debated with very few data. This study provides the first data on the relative speed of the LC for the past 9.2 ka using mean size of the sortable silt of sediments as a proxy from a mid-shelf basin in the western Labrador Sea. LC speed progressively intensified from 9.2-5 ka, during which two meltwater events had minor influence. The LC was fastest between 5 ka and 3.1 ka and gradually weakened after 3.1 ka. The mean size of the sortable silt data shows overall covariations with similar existing data from deep-water areas of the greater North Atlantic, suggesting an overarching link that modulates changes in both the near-surface and deep North Atlantic. A dynamical link between the LC and AMOC vigor is hypothesized in which high meltwater discharge in the Labrador Sea oriented the subpolar gyre (SPG) more North-South (meridional), weakening the SPG, and thus decelerating the upper limb of the AMOC. Conversely, reduction in LC transport during the late Holocene, due to the greater export of sea ice, oriented the SPG more East-West.
... d'Etudes en Géophysique et Océanographie Spatiales, LEGOS-CNES, Observatoire Midi-Pyréné... more ... d'Etudes en Géophysique et Océanographie Spatiales, LEGOS-CNES, Observatoire Midi-Pyrénées, Toulouse, France, [email protected] ... Physical Oceanography Dept., Woods Hole Oceanographic Institution, Woods Hole, MA, USA, [email protected] Chung-yen Kuo ...
The presence of Heinrich layer 3 (HL-3) in the northwest Labrador Sea has been debated in the lit... more The presence of Heinrich layer 3 (HL-3) in the northwest Labrador Sea has been debated in the literature. Calypso giant piston core MD99-2233, five new standard piston cores, and re-interpretation of 34 cores from previous cruises confirm the presence of HL-3 in the Labrador Sea. It is identified by high total carbonate concentration (up to 45%), an increase in coarse fraction content, and lighter N 18 O values in polar species planktonic foraminifer Neogloboquadrina pachyderma (left-coiling) as low as 3.1x. The age of HL-3 of V27 ka was bracketed in the various cores by about 50 14 C-accelerator mass spectrometer dates. Where it is present in ice-proximal regions, it consists of nepheloid-flow deposits at the base and mud turbidites at the top. The thickness of HL-3 varies between 4.8 m (proximal to Hudson Strait) and 0.9 m (distal), decreasing rapidly seaward. On the upper continental slope, HL-3 was too deeply buried to be sampled. Elsewhere, HL-3 is absent in some cores, probably due to slumping or erosion associated with sandy turbidity currents or debris flows.
Logging data are measurements of physical properties of the formation surrounding a borehole, acq... more Logging data are measurements of physical properties of the formation surrounding a borehole, acquired in situ after completion of coring (wireline logging) or during drilling (Logging-While-Drilling, LWD). The range of data (resistivity, gamma radiation, velocity, density, borehole images,…) in any hole depends on the scientific objectives and operational constraints.
Understanding past Atlantic meridional overturning circulation is critical given its pivotal role... more Understanding past Atlantic meridional overturning circulation is critical given its pivotal role in modulating abrupt climate events. However, a lack of accurate estimates of reservoir ages hinders testing the potential synchronicity of abrupt deglacial climate events such as Heinrich massive ice-rafting event 1 (H1) and the Younger Dryas cooling event across the North Atlantic. In this study, we have used the Bermuda Rise core EN120-GGC1, central North Atlantic core CHN82-20, and Integrated Ocean Drilling Program Site 1313. Core CHN82-20 and Site 1313 were collected from the bottom of the western flank of the Mid-Atlantic Ridge and GGC1 from the flank of the Bermuda Rise. Core CHN82-20 and Site 1313 were chosen for their position at the southern margin of the ice-rafted detritus-belt. For the Portuguese margin, we have used records from the high sedimentation rate core MD99-2334K. Twenty five new accelerator mass spectrometer (AMS) 14C dates were used to revise the existing age model of core GGC1 and construct the age model for Site 1313. As a result, we were able to constrain the zonal difference in reservoir ages from 1,200 years in the west to 2,200 years in the northeast Atlantic at ~34oN. Our revised stratigraphy suggests that the onset age for H1 was 16.4 ka. The longer reservoir ages in the northeast Atlantic likely resulted from an upwelling of old deep waters, which were then mixed with the freshwater released by icebergs at the subpolar-subtropical gyre boundary. In contrast, shorter reservoir ages at the Bermuda Rise suggest an intensified subtropical gyre during H1. Our Bermuda Rise data also demonstrate important differences in oxygen-isotope records in three planktonic foraminiferal species. We attribute a δ18O depletion during H1 and enrichment during the Younger Dryas to sea-surface warming and cooling, respectively. Despite this difference, both H1 and YD events were accompanied by an increase in nutrients (Cd/Ca and δ13C in benthic foraminifers) in the Atlantic bottom water, suggesting an incursion of the Southern Ocean waters.
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Its broad intent is to support billions of people worldwide who rely on the oceans for basic needs (Kim 2023). It has been demonstrated that maintaining biodiversity is one of the key pillars to maintaining oceans’ trophic levels (ocean food chain); by extension, it implies a sustainable human food supply. However, the task of selecting appropriate measures of biodiversity that have utility for international ocean management issues will require further study. For example, Harris (2007) notes that “what we now regard as the normal state of the oceans has been severely perturbed by the removal of top predators.” It is also equally important to assess modification caused by unintended introduction of alien species, open ocean aquaculture, range of pharmaceuticals, anthropogenic chemicals, etc.
Its broad intent is to support billions of people worldwide who rely on the oceans for basic needs (Kim 2023). It has been demonstrated that maintaining biodiversity is one of the key pillars to maintaining oceans’ trophic levels (ocean food chain); by extension, it implies a sustainable human food supply. However, the task of selecting appropriate measures of biodiversity that have utility for international ocean management issues will require further study. For example, Harris (2007) notes that “what we now regard as the normal state of the oceans has been severely perturbed by the removal of top predators.” It is also equally important to assess modification caused by unintended introduction of alien species, open ocean aquaculture, range of pharmaceuticals, anthropogenic chemicals, etc.
modulating abrupt climate events. However, a lack of accurate estimates of reservoir ages
hinders testing the potential synchronicity of abrupt deglacial climate events such as Heinrich
massive ice-rafting event 1 (H1) and the Younger Dryas cooling event across the North Atlantic.
In this study, we have used the Bermuda Rise core EN120-GGC1, central North Atlantic core
CHN82-20, and Integrated Ocean Drilling Program Site 1313. Core CHN82-20 and Site 1313
were collected from the bottom of the western flank of the Mid-Atlantic Ridge and GGC1 from
the flank of the Bermuda Rise. Core CHN82-20 and Site 1313 were chosen for their position at
the southern margin of the ice-rafted detritus-belt. For the Portuguese margin, we have used
records from the high sedimentation rate core MD99-2334K. Twenty five new accelerator mass
spectrometer (AMS) 14C dates were used to revise the existing age model of core GGC1 and
construct the age model for Site 1313. As a result, we were able to constrain the zonal difference
in reservoir ages from 1,200 years in the west to 2,200 years in the northeast Atlantic at ~34oN.
Our revised stratigraphy suggests that the onset age for H1 was 16.4 ka. The longer reservoir
ages in the northeast Atlantic likely resulted from an upwelling of old deep waters, which were
then mixed with the freshwater released by icebergs at the subpolar-subtropical gyre boundary.
In contrast, shorter reservoir ages at the Bermuda Rise suggest an intensified subtropical gyre
during H1. Our Bermuda Rise data also demonstrate important differences in oxygen-isotope
records in three planktonic foraminiferal species. We attribute a δ18O depletion during H1 and
enrichment during the Younger Dryas to sea-surface warming and cooling, respectively. Despite
this difference, both H1 and YD events were accompanied by an increase in nutrients (Cd/Ca and
δ13C in benthic foraminifers) in the Atlantic bottom water, suggesting an incursion of the
Southern Ocean waters.