Terrestrial organic carbon is the dominant source of carbon to the SBB with deposition significan... more Terrestrial organic carbon is the dominant source of carbon to the SBB with deposition significantly increasing during flood events. Episodic flood and turbidite remobilization events were responsible for over 25% of the OC buried in the SBB over the past 2,000 years. Drought sedimentation had significantly lower sedimentation rates and had an n-alkane composition consistent with increased marine inputs.
To explore relationships between water column hydrography and foraminiferal geochemistry in the E... more To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δ 18 O and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber, Globigerina bulloides, and Globorotalia menardii, collected from a sediment trap mooring maintained in the Gulf of Tehuantepec from 2006-2012. Differences in δ 18 O between mixed-layer species G. ruber and G. bulloides and thermocline-dweller G. menardii track seasonal changes in upwelling. The records suggest an increase in upwelling during the peak positive phase of El Niño, and an overall reduction in stratification over the six-year period. For all three species, Mg/Ca ratios are higher than what has been reported in previous studies, and show poor correlations to calcification temperature. We suggest that low pH (7.6-8.0) and [CO 3 2− ] values (∼70-120 μmol/kg) in the mixed layer contribute to an overall trend of higher Mg/Ca ratios in this region. Laser Ablation Inductively Coupled Mass Spectrometry analyses of G. bulloides with high Mg/Ca ratios (>9 mmol/mol) reveal the presence of a secondary coating of inorganic calcite that has Mg/Ca and Mn/Ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite, along with elevated Sr/Ca and Ba/Ca ratios. Some of the samples with abnormally high Mg/Ca are found during periods of high primary productivity, suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen-poor waters in the water column. Although similar shell layering has been observed on fossil foraminifera, this is the first time such alteration has been studied in shells collected from the water column. Our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element:calcium ratios prior to deposition on the seafloor, particularly in high-productivity, low-oxygen environments.
The Cariaco Basin is a 1400-m-deep depression approximately 160 km long by 70 km wide located off... more The Cariaco Basin is a 1400-m-deep depression approximately 160 km long by 70 km wide located off the central Venezuelan coast . It is connected to the Atlantic Ocean by a sill ~100-m-deep, and two slightly deeper channels that breech it; Canal Centinela (146-m-deep) and Canal de la Tortuge (135-m-deep). High surface production rates and restricted circulation result in anoxic waters below ca. 275 m. The depth of the oxycline varies between 250 and 320 m and is independent of density. Rather, fluctuations in oxycline depth appear to be due to lateral intrusions of Caribbean Sea water that are linked to eddies along the continental shelf. A mooring with five sediment traps (Z, A-D) is located in the eastern Cariaco Basin. Traps A-D have been in place since November 1995. Trap A is located in oxic waters at 226 ± 6 m. Trap B is located at 407 ± 3 m and Trap D is located at 1205 ± 3 m. Trap C was located at a depth of 880 ± 2 m from Jan. 1996 to Nov. 2000, and was moved to 807 ± 2 m in Nov. 2000. A fifth trap, Z, was added in November 2003 at 110 m for the first 6 months, and at 150 m thereafter. All five sediment traps are coneshaped with a 0.5 m**2 opening that is covered with a baffle top to reduce turbulence. The mooring is deployed for six-month intervals and each sample collection cup is filled with a buffered 3.2% formalin solution as a preservative for the accumulating organic matter. The cups are numbered 1-13, with cup 1 collecting for the two-week interval immediately following deployment, and cup 13 collecting for the 2 weeks immediately before recovery.
Deep Sea Research Part II: Topical Studies in Oceanography, 2013
We examined the variability of sea surface carbon dioxide fugacity (fCO 2sea) and its relation to... more We examined the variability of sea surface carbon dioxide fugacity (fCO 2sea) and its relation to temperature at the Cariaco Basin ocean time-series location (10130 0 N, 64140 0 W) for the period from 1996 through 2008. Periods of warm (positive) and cold (negative) anomalies at the station were related to variability in coastal upwelling intensity. A positive temporal trend in monthlydeseasonalized sea surface temperatures (SST) was observed, leading to an overall increase of 1.13 1C over 13 years. Surface fCO 2sea displayed significant short-term variation (month to month) with a range of 330-445 matm. In addition to a large seasonal range (58 7 17 matm), deseasonalized fCO 2sea data showed an interannual positive trend of 1.77 7 0.43 matm yr À 1. In the Cariaco Basin, positive and negative anomalies of temperature and fCO 2sea are in phase. An increase/decrease of 1 1C coincides with an increase/decrease of 16-20 matm of fCO 2sea. Deseasonalized fCO 2sea normalized to 26.05 1C, the mean Cariaco SST, shows a lower rate of increase (0.51 7 0.49 matm yr À 1). Based on these observations, 72% of the increase in fCO 2sea in Cariaco Basin between 1996 and 2008 can be attributed to an increasing temperature trend of surface waters, making this the primary factor controlling fugacity at this location. During this period, a decrease in upwelling intensity was also observed. The phytoplankton community changed from large diatom-dominated blooms during upwelling in the late 1990's to blooms dominated by smaller cells in the first decade of the 21st century. The average net sea-air CO 2 flux over the study period is 2.0 7 2.6 mol C m À 2 yr À 1 employing the Wanninkhof parameterization, and 2.1 72.5 mol C m À 2 yr À 1 based on Nightingale's model. To further understand the connection between the changes observed in the Cariaco Basin, the relationships between interannual variability in the temperature anomaly with three modes of climate variability (AMO, NAO and ENSO) were examined. The correlations between SSTA and two of these climate modes (AMO and ENSO) only show very weak relationships, although they were significant.
The Cariaco Basin, historically a natural laboratory for biogeochemists, also contains a record o... more The Cariaco Basin, historically a natural laboratory for biogeochemists, also contains a record of past climate change. Under interglacial conditions, the formation of sediment varves at the bottom of the basin is related to variability near the ocean's surface, and appears to reflect variations on the scale of the Atlantic Ocean. The CARIACO (CArbon Retention In A Colored Ocean) program
Biweekly sediment trap samples have been collected continuously since 1995 at multiple depths in ... more Biweekly sediment trap samples have been collected continuously since 1995 at multiple depths in the water column as part of the Cariaco Basin ocean time series. A selected set of samples of sinking particulate matter from 1997 to 1999 have been analyzed by alkaline CuO oxidation to measure the fluxes of lignin phenol products. Since lignin is uniquely derived from
A combination of high-resolution and wide-field imaging reveals two binary stars and one triple s... more A combination of high-resolution and wide-field imaging reveals two binary stars and one triple star system among the sample of the first 11 stars with planets detected by radial velocity variations. High resolution speckle or adaptive optics (AO) data probe subarcsecond scales down to the diffraction limit of the Keck 10-m or the Lick 3-m, and direct images or AO images are sensitive to a wider field, extending to 10" or 38", depending upon the camera. One of the binary systems-HD 114762-was not previously known to be a spatially resolved multiple system; additional data taken with the combination of Keck adaptive optics and NIRSPEC are used to characterize the new companion. The second binary system-Tau Boo-was a known multiple with two conflicting orbital solutions; the current data will help constrain the discrepant estimates of periastron time and separation. Another target-16 Cyg Bwas a known common proper motion binary, but the current data resolve a new third component, close to the wide companion 16 Cyg A. Both the HD 114762 and 16 Cyg B systems harbor planets in eccentric orbits, while the Tau Boo binary contains an extremely close planet in a tidally-circularized orbit. Although the sample is currently small, the proportion of binary systems is comparable to that measured in the field over a similar separation range. Incorporating the null result from another companion search project lowers the overall fraction of planets in binary systems, but the detections in our survey reveal that planets can form in binaries separated by less than 50 AU.
Continental margins play an important role in the global carbon cycle, accounting for about 10-15... more Continental margins play an important role in the global carbon cycle, accounting for about 10-15% of the carbon produced in oceanic systems, and 40% of carbon deposition on the global ocean floor. In an effort to understand some of the processes operating along a wind-driven coastal upwelling margin, the CARIACO time-series project (CArbon Retention In A Colored Ocean) has carried
ABSTRACT The Cariaco Basin, Venezuela is well-positioned to record a detailed history of surface ... more ABSTRACT The Cariaco Basin, Venezuela is well-positioned to record a detailed history of surface ocean changes along the southern margin of the Caribbean and the tropical Atlantic. Varved, high deposition rate sediments deposited under anoxic conditions and an abundance of well-preserved microfossils result in one of the few marine records capable of preserving evidence of interannual- to decadal-scale climate variability in the tropical Atlantic. Boreal winter/spring sea surface temperatures (SST) spanning the last eight centuries have previously been reconstructed using Mg/Ca measurements on the planktic foraminifer Globigerina bulloides. Here we present the complementary record using Globigerinoides ruber (pink), a summer/fall indicator. Globigerinoides ruber Mg/Ca values are generally greater than those of G. bulloides from the same sample, reflecting warmer calcification temperatures. Both species' records display similar long-term trends, yet there are some distinctive differences. The Medieval Warm Period (MWP) and Little Ice Age (LIA) as distinctly separate climate events are more apparent in the G. ruber record than that of G. bulloides. Additionally, greater variability in the G. ruber data may indicate a stronger than expected bias from productivity during the local upwelling season. As G. bulloides and pink G. ruber are thought to be winter/spring and summer/fall SST indicators, respectively (albeit with the potential upwelling season bias), the intersample differences between the two records can potentially be interpreted as a record of seasonality. Our seasonality reconstruction shows a distinctive oscillation of 4 °C with a period of approximately 200 years. The proxy seasonality is slightly less than what has been instrumentally measured (5 to 6 °C) over the last 15 years, and does not appear related to or affected by the MWP or LIA events.
We present a 2.5-year-long sediment trap record of dinoflagellate cyst production in the Cariaco ... more We present a 2.5-year-long sediment trap record of dinoflagellate cyst production in the Cariaco Basin, off Venezuela (southern Caribbean Sea). The site lies under the influence of wind-driven, seasonal upwelling which promotes high levels of primary productivity during boreal winter and spring. Changes in dinoflagellate cyst production is documented between November 1996 and May 1999 at ∼ 14-day intervals and interpreted in the context of in situ observations of physico-chemical and biological parameters measured at the mooring site. Dinoflagellate cyst assemblages are diverse (57 taxa) and dominated by cyst taxa of heterotrophic affinity, primarily Brigantedinium spp. (51 % of the total trap assemblage). Average cyst fluxes to the trap are high (17.1 × 10 3 cysts m −2 day −1) and show great seasonal and interannual variability. On seasonal timescales, dinoflagellate cyst production responds closely to variations in upwelling strength, with increases in cyst fluxes of several protoperidinioid taxa observed during active upwelling intervals, predominantly Brigantedinium spp. Cyst taxa produced by autotrophic dinoflagellates, in particular Bitectatodinium spongium, also respond positively to upwelling. Several "spiny brown" cysts contribute substantially to the assemblages, including Echinidinium delicatum (9.7 %) and Echinidinium granulatum (7.3 %), and show a closer affinity to weaker upwelling conditions. The strong El Niño event of 1997/98 appears to have negatively impacted cyst production in the basin with a 1-year lag, and may have contributed to the unusually high fluxes of cysts type "Cp" (possibly the cysts of the toxic dinoflagellate Cochlodinium polykrikoides sensu Li et al., 2015), with cyst type Cp fluxes up to 11.8 × 10 3 cysts m −2 day −1 observed during the weak upwelling event of February-May 1999. Possible trophic interactions between dinoflagellates and other major planktonic groups are also investigated by comparing the timing and magnitude of cyst production with proxies for phytoplanktonic communities (from photopigment data) and micro-to macrozooplankton abundance indicators (from palynological data) at the site. This work provides new, detailed insights into the ecology of cystproducing dinoflagellates and will allow for more detailed interpretations of fossil assemblages extracted from sedimentary records in the basin and elsewhere.
TheCARIACO(Carbon Retention in a Colored Ocean) Ocean Time-Series Program station, located at 10.... more TheCARIACO(Carbon Retention in a Colored Ocean) Ocean Time-Series Program station, located at 10.50°N, 64.66°W, observed biogeochemical and ecological processes in the Cariaco Basin of the southwestern Caribbean Sea from November 1995 to January 2017. The program completed 232 monthly core cruises, 40 sediment trap deployment cruises, and 40 microbiogeochemical process cruises. Upwelling along the southern Caribbean Sea occurs from approximately November to August. High biological productivity (320-628 g C m y) leads to large vertical fluxes of particulate organic matter, but only approximately 9-10 g C m y fall to the bottom sediments (∼1-3% of primary production). A diverse community of heterotrophic and chemoautotrophic microorganisms, viruses, and protozoa thrives within the oxic-anoxic interface. A decrease in upwelling intensity from approximately 2003 to 2013 and the simultaneous overfishing of sardines in the region led to diminished phytoplankton bloom intensities, increase...
The U.S. Geological Survey anchored a sediment trap in the northern Gulf of Mexico beginning in 2... more The U.S. Geological Survey anchored a sediment trap in the northern Gulf of Mexico beginning in 2008 to collect seasonal time-series data on the flux and assemblage composition of live planktic foraminifers. This report provides an update of the previous time-series data to include results from 2012. Ten species, or varieties, constituted ~92 percent of the 2012 assemblage: Globigerinoides ruber (pink and white varieties), Globigerinoides sacculifer, Globigerina calida, Globigerinella aequilateralis, Globorotalia menardii group [The Gt. menardii group includes Gt. menardii, Gt. tumida, and Gt. ungulata], Orbulina universa, Globorotalia truncatulinoides, Pulleniatina spp., and Neogloboquadrina dutertrei. The mean daily flux was 158 tests per square meter per day (m-2 day-1), with maximum fluxes of >450 tests m-2 day-1 during the beginning of July and mid-August and minimum fluxes of <10 tests m-2 day-1 during the beginning of February and mid-July. Globorotalia truncatulinoides showed a clear preference for the winter, consistent with data from 2008 to 2011. Globigerinoides ruber (white) flux data for 2012 (average 23 tests m-2 day-1) were consistent with data from 2011 (average 30 tests m-2 day-1) and 2010 (average 29 tests m-2 day-1) and showed a steady threefold increase since 2009 (average 11 tests m-2 day-1) and a tenfold increase from the 2008 flux (3 tests m-2 day-1).
To explore relationships between water column hydrography and foraminiferal geochemistry in the E... more To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δ 18 O and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber, Globigerina bulloides, and Globorotalia menardii, collected from a sediment trap mooring maintained in the Gulf of Tehuantepec from 2006-2012. Differences in δ 18 O between mixed-layer species G. ruber and G. bulloides and thermocline-dweller G. menardii track seasonal changes in upwelling. The records suggest an increase in upwelling during the peak positive phase of El Niño, and an overall reduction in stratification over the six-year period. For all three species, Mg/Ca ratios are higher than what has been reported in previous studies, and show poor correlations to calcification temperature. We suggest that low pH (7.6-8.0) and [CO 3 2− ] values (∼70-120 μmol/kg) in the mixed layer contribute to an overall trend of higher Mg/Ca ratios in this region. Laser Ablation Inductively Coupled Mass Spectrometry analyses of G. bulloides with high Mg/Ca ratios (>9 mmol/mol) reveal the presence of a secondary coating of inorganic calcite that has Mg/Ca and Mn/Ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite, along with elevated Sr/Ca and Ba/Ca ratios. Some of the samples with abnormally high Mg/Ca are found during periods of high primary productivity, suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen-poor waters in the water column. Although similar shell layering has been observed on fossil foraminifera, this is the first time such alteration has been studied in shells collected from the water column. Our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element:calcium ratios prior to deposition on the seafloor, particularly in high-productivity, low-oxygen environments.
Due to their high topographic relief and susceptibility to erosion, mountainous coastal rivers ma... more Due to their high topographic relief and susceptibility to erosion, mountainous coastal rivers may potentially deliver high sediment and organic matter loads to continental margins. Three small mountainous rivers (Manzanares, Neveri and Unare) that empty onto the shelf of the eastern Cariaco Basin (Venezuela) were examined during the rainy season in September 2003 and 2006 under the framework of the
Terrestrial organic carbon is the dominant source of carbon to the SBB with deposition significan... more Terrestrial organic carbon is the dominant source of carbon to the SBB with deposition significantly increasing during flood events. Episodic flood and turbidite remobilization events were responsible for over 25% of the OC buried in the SBB over the past 2,000 years. Drought sedimentation had significantly lower sedimentation rates and had an n-alkane composition consistent with increased marine inputs.
To explore relationships between water column hydrography and foraminiferal geochemistry in the E... more To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δ 18 O and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber, Globigerina bulloides, and Globorotalia menardii, collected from a sediment trap mooring maintained in the Gulf of Tehuantepec from 2006-2012. Differences in δ 18 O between mixed-layer species G. ruber and G. bulloides and thermocline-dweller G. menardii track seasonal changes in upwelling. The records suggest an increase in upwelling during the peak positive phase of El Niño, and an overall reduction in stratification over the six-year period. For all three species, Mg/Ca ratios are higher than what has been reported in previous studies, and show poor correlations to calcification temperature. We suggest that low pH (7.6-8.0) and [CO 3 2− ] values (∼70-120 μmol/kg) in the mixed layer contribute to an overall trend of higher Mg/Ca ratios in this region. Laser Ablation Inductively Coupled Mass Spectrometry analyses of G. bulloides with high Mg/Ca ratios (>9 mmol/mol) reveal the presence of a secondary coating of inorganic calcite that has Mg/Ca and Mn/Ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite, along with elevated Sr/Ca and Ba/Ca ratios. Some of the samples with abnormally high Mg/Ca are found during periods of high primary productivity, suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen-poor waters in the water column. Although similar shell layering has been observed on fossil foraminifera, this is the first time such alteration has been studied in shells collected from the water column. Our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element:calcium ratios prior to deposition on the seafloor, particularly in high-productivity, low-oxygen environments.
The Cariaco Basin is a 1400-m-deep depression approximately 160 km long by 70 km wide located off... more The Cariaco Basin is a 1400-m-deep depression approximately 160 km long by 70 km wide located off the central Venezuelan coast . It is connected to the Atlantic Ocean by a sill ~100-m-deep, and two slightly deeper channels that breech it; Canal Centinela (146-m-deep) and Canal de la Tortuge (135-m-deep). High surface production rates and restricted circulation result in anoxic waters below ca. 275 m. The depth of the oxycline varies between 250 and 320 m and is independent of density. Rather, fluctuations in oxycline depth appear to be due to lateral intrusions of Caribbean Sea water that are linked to eddies along the continental shelf. A mooring with five sediment traps (Z, A-D) is located in the eastern Cariaco Basin. Traps A-D have been in place since November 1995. Trap A is located in oxic waters at 226 ± 6 m. Trap B is located at 407 ± 3 m and Trap D is located at 1205 ± 3 m. Trap C was located at a depth of 880 ± 2 m from Jan. 1996 to Nov. 2000, and was moved to 807 ± 2 m in Nov. 2000. A fifth trap, Z, was added in November 2003 at 110 m for the first 6 months, and at 150 m thereafter. All five sediment traps are coneshaped with a 0.5 m**2 opening that is covered with a baffle top to reduce turbulence. The mooring is deployed for six-month intervals and each sample collection cup is filled with a buffered 3.2% formalin solution as a preservative for the accumulating organic matter. The cups are numbered 1-13, with cup 1 collecting for the two-week interval immediately following deployment, and cup 13 collecting for the 2 weeks immediately before recovery.
Deep Sea Research Part II: Topical Studies in Oceanography, 2013
We examined the variability of sea surface carbon dioxide fugacity (fCO 2sea) and its relation to... more We examined the variability of sea surface carbon dioxide fugacity (fCO 2sea) and its relation to temperature at the Cariaco Basin ocean time-series location (10130 0 N, 64140 0 W) for the period from 1996 through 2008. Periods of warm (positive) and cold (negative) anomalies at the station were related to variability in coastal upwelling intensity. A positive temporal trend in monthlydeseasonalized sea surface temperatures (SST) was observed, leading to an overall increase of 1.13 1C over 13 years. Surface fCO 2sea displayed significant short-term variation (month to month) with a range of 330-445 matm. In addition to a large seasonal range (58 7 17 matm), deseasonalized fCO 2sea data showed an interannual positive trend of 1.77 7 0.43 matm yr À 1. In the Cariaco Basin, positive and negative anomalies of temperature and fCO 2sea are in phase. An increase/decrease of 1 1C coincides with an increase/decrease of 16-20 matm of fCO 2sea. Deseasonalized fCO 2sea normalized to 26.05 1C, the mean Cariaco SST, shows a lower rate of increase (0.51 7 0.49 matm yr À 1). Based on these observations, 72% of the increase in fCO 2sea in Cariaco Basin between 1996 and 2008 can be attributed to an increasing temperature trend of surface waters, making this the primary factor controlling fugacity at this location. During this period, a decrease in upwelling intensity was also observed. The phytoplankton community changed from large diatom-dominated blooms during upwelling in the late 1990's to blooms dominated by smaller cells in the first decade of the 21st century. The average net sea-air CO 2 flux over the study period is 2.0 7 2.6 mol C m À 2 yr À 1 employing the Wanninkhof parameterization, and 2.1 72.5 mol C m À 2 yr À 1 based on Nightingale's model. To further understand the connection between the changes observed in the Cariaco Basin, the relationships between interannual variability in the temperature anomaly with three modes of climate variability (AMO, NAO and ENSO) were examined. The correlations between SSTA and two of these climate modes (AMO and ENSO) only show very weak relationships, although they were significant.
The Cariaco Basin, historically a natural laboratory for biogeochemists, also contains a record o... more The Cariaco Basin, historically a natural laboratory for biogeochemists, also contains a record of past climate change. Under interglacial conditions, the formation of sediment varves at the bottom of the basin is related to variability near the ocean&amp;amp;amp;amp;amp;#39;s surface, and appears to reflect variations on the scale of the Atlantic Ocean. The CARIACO (CArbon Retention In A Colored Ocean) program
Biweekly sediment trap samples have been collected continuously since 1995 at multiple depths in ... more Biweekly sediment trap samples have been collected continuously since 1995 at multiple depths in the water column as part of the Cariaco Basin ocean time series. A selected set of samples of sinking particulate matter from 1997 to 1999 have been analyzed by alkaline CuO oxidation to measure the fluxes of lignin phenol products. Since lignin is uniquely derived from
A combination of high-resolution and wide-field imaging reveals two binary stars and one triple s... more A combination of high-resolution and wide-field imaging reveals two binary stars and one triple star system among the sample of the first 11 stars with planets detected by radial velocity variations. High resolution speckle or adaptive optics (AO) data probe subarcsecond scales down to the diffraction limit of the Keck 10-m or the Lick 3-m, and direct images or AO images are sensitive to a wider field, extending to 10" or 38", depending upon the camera. One of the binary systems-HD 114762-was not previously known to be a spatially resolved multiple system; additional data taken with the combination of Keck adaptive optics and NIRSPEC are used to characterize the new companion. The second binary system-Tau Boo-was a known multiple with two conflicting orbital solutions; the current data will help constrain the discrepant estimates of periastron time and separation. Another target-16 Cyg Bwas a known common proper motion binary, but the current data resolve a new third component, close to the wide companion 16 Cyg A. Both the HD 114762 and 16 Cyg B systems harbor planets in eccentric orbits, while the Tau Boo binary contains an extremely close planet in a tidally-circularized orbit. Although the sample is currently small, the proportion of binary systems is comparable to that measured in the field over a similar separation range. Incorporating the null result from another companion search project lowers the overall fraction of planets in binary systems, but the detections in our survey reveal that planets can form in binaries separated by less than 50 AU.
Continental margins play an important role in the global carbon cycle, accounting for about 10-15... more Continental margins play an important role in the global carbon cycle, accounting for about 10-15% of the carbon produced in oceanic systems, and 40% of carbon deposition on the global ocean floor. In an effort to understand some of the processes operating along a wind-driven coastal upwelling margin, the CARIACO time-series project (CArbon Retention In A Colored Ocean) has carried
ABSTRACT The Cariaco Basin, Venezuela is well-positioned to record a detailed history of surface ... more ABSTRACT The Cariaco Basin, Venezuela is well-positioned to record a detailed history of surface ocean changes along the southern margin of the Caribbean and the tropical Atlantic. Varved, high deposition rate sediments deposited under anoxic conditions and an abundance of well-preserved microfossils result in one of the few marine records capable of preserving evidence of interannual- to decadal-scale climate variability in the tropical Atlantic. Boreal winter/spring sea surface temperatures (SST) spanning the last eight centuries have previously been reconstructed using Mg/Ca measurements on the planktic foraminifer Globigerina bulloides. Here we present the complementary record using Globigerinoides ruber (pink), a summer/fall indicator. Globigerinoides ruber Mg/Ca values are generally greater than those of G. bulloides from the same sample, reflecting warmer calcification temperatures. Both species&#39; records display similar long-term trends, yet there are some distinctive differences. The Medieval Warm Period (MWP) and Little Ice Age (LIA) as distinctly separate climate events are more apparent in the G. ruber record than that of G. bulloides. Additionally, greater variability in the G. ruber data may indicate a stronger than expected bias from productivity during the local upwelling season. As G. bulloides and pink G. ruber are thought to be winter/spring and summer/fall SST indicators, respectively (albeit with the potential upwelling season bias), the intersample differences between the two records can potentially be interpreted as a record of seasonality. Our seasonality reconstruction shows a distinctive oscillation of 4 °C with a period of approximately 200 years. The proxy seasonality is slightly less than what has been instrumentally measured (5 to 6 °C) over the last 15 years, and does not appear related to or affected by the MWP or LIA events.
We present a 2.5-year-long sediment trap record of dinoflagellate cyst production in the Cariaco ... more We present a 2.5-year-long sediment trap record of dinoflagellate cyst production in the Cariaco Basin, off Venezuela (southern Caribbean Sea). The site lies under the influence of wind-driven, seasonal upwelling which promotes high levels of primary productivity during boreal winter and spring. Changes in dinoflagellate cyst production is documented between November 1996 and May 1999 at ∼ 14-day intervals and interpreted in the context of in situ observations of physico-chemical and biological parameters measured at the mooring site. Dinoflagellate cyst assemblages are diverse (57 taxa) and dominated by cyst taxa of heterotrophic affinity, primarily Brigantedinium spp. (51 % of the total trap assemblage). Average cyst fluxes to the trap are high (17.1 × 10 3 cysts m −2 day −1) and show great seasonal and interannual variability. On seasonal timescales, dinoflagellate cyst production responds closely to variations in upwelling strength, with increases in cyst fluxes of several protoperidinioid taxa observed during active upwelling intervals, predominantly Brigantedinium spp. Cyst taxa produced by autotrophic dinoflagellates, in particular Bitectatodinium spongium, also respond positively to upwelling. Several "spiny brown" cysts contribute substantially to the assemblages, including Echinidinium delicatum (9.7 %) and Echinidinium granulatum (7.3 %), and show a closer affinity to weaker upwelling conditions. The strong El Niño event of 1997/98 appears to have negatively impacted cyst production in the basin with a 1-year lag, and may have contributed to the unusually high fluxes of cysts type "Cp" (possibly the cysts of the toxic dinoflagellate Cochlodinium polykrikoides sensu Li et al., 2015), with cyst type Cp fluxes up to 11.8 × 10 3 cysts m −2 day −1 observed during the weak upwelling event of February-May 1999. Possible trophic interactions between dinoflagellates and other major planktonic groups are also investigated by comparing the timing and magnitude of cyst production with proxies for phytoplanktonic communities (from photopigment data) and micro-to macrozooplankton abundance indicators (from palynological data) at the site. This work provides new, detailed insights into the ecology of cystproducing dinoflagellates and will allow for more detailed interpretations of fossil assemblages extracted from sedimentary records in the basin and elsewhere.
TheCARIACO(Carbon Retention in a Colored Ocean) Ocean Time-Series Program station, located at 10.... more TheCARIACO(Carbon Retention in a Colored Ocean) Ocean Time-Series Program station, located at 10.50°N, 64.66°W, observed biogeochemical and ecological processes in the Cariaco Basin of the southwestern Caribbean Sea from November 1995 to January 2017. The program completed 232 monthly core cruises, 40 sediment trap deployment cruises, and 40 microbiogeochemical process cruises. Upwelling along the southern Caribbean Sea occurs from approximately November to August. High biological productivity (320-628 g C m y) leads to large vertical fluxes of particulate organic matter, but only approximately 9-10 g C m y fall to the bottom sediments (∼1-3% of primary production). A diverse community of heterotrophic and chemoautotrophic microorganisms, viruses, and protozoa thrives within the oxic-anoxic interface. A decrease in upwelling intensity from approximately 2003 to 2013 and the simultaneous overfishing of sardines in the region led to diminished phytoplankton bloom intensities, increase...
The U.S. Geological Survey anchored a sediment trap in the northern Gulf of Mexico beginning in 2... more The U.S. Geological Survey anchored a sediment trap in the northern Gulf of Mexico beginning in 2008 to collect seasonal time-series data on the flux and assemblage composition of live planktic foraminifers. This report provides an update of the previous time-series data to include results from 2012. Ten species, or varieties, constituted ~92 percent of the 2012 assemblage: Globigerinoides ruber (pink and white varieties), Globigerinoides sacculifer, Globigerina calida, Globigerinella aequilateralis, Globorotalia menardii group [The Gt. menardii group includes Gt. menardii, Gt. tumida, and Gt. ungulata], Orbulina universa, Globorotalia truncatulinoides, Pulleniatina spp., and Neogloboquadrina dutertrei. The mean daily flux was 158 tests per square meter per day (m-2 day-1), with maximum fluxes of >450 tests m-2 day-1 during the beginning of July and mid-August and minimum fluxes of <10 tests m-2 day-1 during the beginning of February and mid-July. Globorotalia truncatulinoides showed a clear preference for the winter, consistent with data from 2008 to 2011. Globigerinoides ruber (white) flux data for 2012 (average 23 tests m-2 day-1) were consistent with data from 2011 (average 30 tests m-2 day-1) and 2010 (average 29 tests m-2 day-1) and showed a steady threefold increase since 2009 (average 11 tests m-2 day-1) and a tenfold increase from the 2008 flux (3 tests m-2 day-1).
To explore relationships between water column hydrography and foraminiferal geochemistry in the E... more To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δ 18 O and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber, Globigerina bulloides, and Globorotalia menardii, collected from a sediment trap mooring maintained in the Gulf of Tehuantepec from 2006-2012. Differences in δ 18 O between mixed-layer species G. ruber and G. bulloides and thermocline-dweller G. menardii track seasonal changes in upwelling. The records suggest an increase in upwelling during the peak positive phase of El Niño, and an overall reduction in stratification over the six-year period. For all three species, Mg/Ca ratios are higher than what has been reported in previous studies, and show poor correlations to calcification temperature. We suggest that low pH (7.6-8.0) and [CO 3 2− ] values (∼70-120 μmol/kg) in the mixed layer contribute to an overall trend of higher Mg/Ca ratios in this region. Laser Ablation Inductively Coupled Mass Spectrometry analyses of G. bulloides with high Mg/Ca ratios (>9 mmol/mol) reveal the presence of a secondary coating of inorganic calcite that has Mg/Ca and Mn/Ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite, along with elevated Sr/Ca and Ba/Ca ratios. Some of the samples with abnormally high Mg/Ca are found during periods of high primary productivity, suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen-poor waters in the water column. Although similar shell layering has been observed on fossil foraminifera, this is the first time such alteration has been studied in shells collected from the water column. Our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element:calcium ratios prior to deposition on the seafloor, particularly in high-productivity, low-oxygen environments.
Due to their high topographic relief and susceptibility to erosion, mountainous coastal rivers ma... more Due to their high topographic relief and susceptibility to erosion, mountainous coastal rivers may potentially deliver high sediment and organic matter loads to continental margins. Three small mountainous rivers (Manzanares, Neveri and Unare) that empty onto the shelf of the eastern Cariaco Basin (Venezuela) were examined during the rainy season in September 2003 and 2006 under the framework of the
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