The phase relationship between climate parameters during terminations gives insight into deglacia... more The phase relationship between climate parameters during terminations gives insight into deglaciation mechanisms. By combining foraminiferal Mg/Ca and alkenone thermometers with planktonic and benthic foraminiferal δ18O, we determined the phase relationship between local sea surface temperature (SST) and global seawater δ18O changes in the Coral Sea in the Southwestern Pacific over the last 360 ka. The onset of the SST warming preceded the seawater δ18O change by several ka for Termination I, II and III. During Termination I, the SST warming started at 20 ka BP, earlier than atmospheric CO 2 rise suggesting that the greenhouse effect was not the main trigger of this early warming. Compilation of 14C-dated SST records from the whole Pacific during Termination I reveals that the onset of the warming is generally earlier in the Southern and the tropical Pacific than in the North Pacific. This spatio-temporal warming pattern suggests linkage between the southern ocean and tropical Pacific. The early tropical warming could provide heat and moisture to the northern high latitudes, modifying radiative balance and precipitation over ice sheets at the onset of deglaciation.
The magnetic and geochemical properties of four marine sediment cores from the North-Western Amer... more The magnetic and geochemical properties of four marine sediment cores from the North-Western American margin allowed reconstructing the dynamics of the terrigenous sedimentation, related to climatic changes during the last glacial-interglacial cycle (0-120,000 yrs). The cores have been retrieved in three sites located on the Californian and Mexican coasts: Santa Barbara Basin (35°N), margin of Baja California (23°N) and Gulf of Tehuantepec (15°N). The present sedimentation is characterized by high terrigenous input, deposited under the influence of a strong seasonal variability and high accumulation rates (35 to 150 cm/ka), allowing to monitor the rhythms of the terrigenous input at high resolution. The magnetic parameters (magnetic susceptibility, natural, anhysteretic and isothermal remanent magnetizations and hysteresis properties) are used to trace the concentration, nature or grain sizes changes of the magnetic fraction. The type of terrigenous iron oxides and grain sizes identified (magnetite, hematite, goethite) can be related to fluvial or aeolian inputs, and thus to erosion regimes forced by climatic conditions. The relative contents of major and trace elements, measured by X-ray fluorescence scanner (XRF) on key interval of the cores, helped to improve interpretations. The sedimentary sequences, dated by correlation of magnetic susceptibility profiles, calibrated 14C ages and identification of paleomagnetic excursions, totally or partly cover the last glacial-interglacial cycle (0-120 ka). The high concentration of iron oxides in glacial sediments in the three sites suggests strong terrigenous inputs on the NW American margin and notably intense aeolian inputs during the last glacial maximum (20-26 ka BP), revealing a strong erosion in arid conditions affecting wider areas of coastal surfaces (lower sea level). In the Santa Barbara Basin, terrigenous input variations during the last 35 ka were probably modulated by the oscillation of the volume and spatial extension of the North American (Laurentide) Ice cap. The sedimentary sequence off Southern Baja California peninsula covers the last 120 ka and reveals that the fluvial inputs are related to climatic variability of North Atlantic whilst the aeolian inputs are driven by the shifts of the low pressure cells belonging to the North Mexican Monsoon, under direct control of the summer insolation at 23°N. In the Gulf of Tehuantepec, aeolian and fluvial inputs are synchronous over the last 40 ka and may be modulated by both the Trade winds intensity and precipitation regimes.
The western Pacific warm pool (WPWP) is an important heat source for the atmospheric circulation ... more The western Pacific warm pool (WPWP) is an important heat source for the atmospheric circulation and influences climate conditions worldwide. Estimating WPWP sensitivity to past radiative forcing perturbations is important for understanding the magnitudes and patterns of current and projected tropical climate change. Here we present a new Mg/Ca-based sea surface temperature (SST) reconstruction over the past 400 ka from the Bismarck Sea, off Papua New Guinea, along with benthic foraminiferal d 18 O records and a transient intermediate complexity earth system model simulation. The Mg/Ca-SST record exhibits a close similarity with atmospheric CO 2 content for the whole study period. Our model analysis demonstrates that greenhouse gas forcing is the primary driver for glacial/interglacial SST changes in the entire WPWP region. Mg/Ca-SST in the Bismarck Sea also includes a weaker precessional component, which covaries with reconstructed and simulated local precipitation, and simulated surface currents. We propose that orbitally driven latitudinal shifts of the Intertropical Convergence Zone and oceanic heat advection are responsible for this residual SST variability. On glacial timescales the reconstructed WPWP surface temperature changes over the past 400 ka are highly correlated with East Antarctic air temperature variations. The strong effect of greenhouse gas forcings on both records and on global mean temperature variability allows us to determine a scaling factor of 1e1.5 between reconstructed WPWP temperature anomalies and estimates of the global mean temperature.
ABSTRACT Change in past global surface temperature (ΔT) in relation to radiative forcing provides... more ABSTRACT Change in past global surface temperature (ΔT) in relation to radiative forcing provides key information on ongoing global warming. Compilation of extensive paleo-reconstruction and modeling effort have contributed to better constraining ΔT. Another approach is to study in detail specific regions that reflect global signal. Western Pacific Warm Pool (WPWP) is one of the targets since the Sea Surface Temperature (SST) in the WPWP is mainly determined thermodynamically and a tight correlation between tropical SST and global signal is expected. However, highly resolved paleo-SST records have been limited in marginal seas where local effects interfered. Here we present the past 400 kyr SST reconstruction based on planktonic foraminiferal Mg/Ca from a marine sediment in the north of the New Guinea Island, the centre of the present WPWP. Striking similarity and synchronism between the SST, the benthic foraminiferal δ18O of the same core, and the atmospheric CO2 records from Antarctic ice cores indicate that the WPWP SST primarily reflected global signal. A strong linear relationship between the SST and ΔT based on Antarctic temperature further confirms the usefulness of WPWP SST. Obtained SST-based ΔT is coupled with past greenhouse gas and ice sheet albedo forcing to quantify climate sensitivity. This yields 2.4±0.8°C, which agrees well with the recent estimate of 2.3°C. Within uncertainty, glacial and interglacial data give comparable climate sensitivity, suggesting that the impact of climate background would be minor or the current dataset failed to detect the difference because of the large uncertainty.
ABSTRACT Latitudinal movements of the Intertropical Convergence Zone (ITCZ), analogous to its pre... more ABSTRACT Latitudinal movements of the Intertropical Convergence Zone (ITCZ), analogous to its present-day seasonal shifts, and El Niño Southern Oscillation (ENSO)-type interannual variability both potentially impacted the tropical Pacific hydrology during the last glacial period. However, changes in ENSO activity and in the ITCZ dynamics are difficult to disentangle from paleoceanographic reconstructions because they are both embedded in the tropical hydrological signal derived from marine sediment cores. In this presentation we will compare tropical Pacific sedimentary records of paleoprecipitation to decipher which climate mechanism was responsible for the past rainfall changes. We suggest that latitudinal movements of the ITCZ are consistent with the observed rainfall patterns, challenging the ENSO hypothesis for explaining the rapid rainfall changes at low latitudes. The ITCZ-related mechanism appears to reflect large-scale atmospheric rearrangements over the tropical belt, with a pronounced Heinrich-Dansgaard/Oeschger signature. This observation is coherent with the simulated tropical rainfall anomalies induced by a weakening of the Atlantic thermohaline circulation in modeling experiments. This result further implies that changes in ENSO variability are difficult to extract from paleoceanographic reconstructions because they are superimposed on changes in seasonal variability that modulate the first-order climate signal. We circumvent this difficulty by reconstructing thermocline structure from a key sediment core retrieved from the eastern equatorial Pacific. At the core location, changes in hydrologic parameters within the thermocline are linked to ENSO activity, with a reduced influence of seasonal variability compared to surface waters. We performed repeated isotopic analyses (d18O) on single specimens of the thermocline-dwelling planktonic foraminifera Neogloboquadrina dutertrei at several targeted time periods over the last 50 ka to extract the total thermocline variance, a parameter supposed to reveal changes in ENSO. No fundamental changes in amplitude and frequency of the events were detected despite differences in climatic background. However, our data suggest that long-term variations at the thermocline occurred over the last 50 ka, with the highest and lowest ENSO activities occurring during the last glacial period and the Last Glacial Maximum, respectively.
The Levant, influenced by both the Mediterranean Sea and the Saharan–Arabian deserts, is a key re... more The Levant, influenced by both the Mediterranean Sea and the Saharan–Arabian deserts, is a key region for understanding climatic changes in response to glacial/interglacial boundary conditions that have greatly affected regional hydrology. Here, we present the first long-term paleoenvironmental record from the northern Levant, presently much wetter than the southern Levant. Our record derives from the multi-proxy study of a
Holocene Eastern Mediterranean Sea sediments contain an organic-rich sapropel S1 layer that was f... more Holocene Eastern Mediterranean Sea sediments contain an organic-rich sapropel S1 layer that was formed in oxygen-depleted waters. The spatial distribution of this layer revealed that during S1 deposition deep waters were permanently anoxic below 1800 m in water depth. To provide further insight into past Eastern Mediterranean Sea circulation, a multi-proxy approach was applied to a core retrieved close to the 1800 m boundary (at 1780 m). We measured the bulk sediment elemental composition, the stable isotopic composition of the planktonic foraminifer <i>Globigerinoides ruber</i>, and the abundance of benthic foraminifera since the last deglaciation. The result indicates that authigenic U and Mo accumulation began around 13–12 cal ka BP, in concert with surface water freshening estimated from the <i>G. ruber</i> δ<sup>18</sup>O record. The onset of bottom/pore water oxygen depletion occurred prior to S1 deposition inferred from barium enrichment. I...
The low-latitude hydrological cycle is a key climate parameter on different timescales, as it con... more The low-latitude hydrological cycle is a key climate parameter on different timescales, as it contributes to various feedback processes. Modelling studies suggest that the interhemispheric insolation contrast is the major factor controlling the cycle, although the influence of glacial conditions and the phase relationships relative to insolation forcing remain undetermined. In this work, we studied precipitation variability over Papua New Guinea (PNG, 3 S) for the past 400 ka using terrigenous fractions transported by the Sepik River to the Western Pacific Warm Pool (WPWP). A multi-decadal to centennial resolution of the elemental content was obtained using X-ray fluorescence scanning of a marine sediment core using an age model based on 14 C dates and benthic foraminiferal d 18 O. Indicators of the coarse river particulate fraction (bulk and CaCO 3 -free basis Ti concentrations, the log intensity ratios of Ti/K and Ti/Ca) displayed a dominant 23 ka periodicity without a clear glacialeinterglacial trend. Our precipitation records showed a tight relationship with local summer insolation (3 S, January) with time-dependent lag of 0 to 4 ka.
The phase relationship between climate parameters during terminations gives insight into deglacia... more The phase relationship between climate parameters during terminations gives insight into deglaciation mechanisms. By combining foraminiferal Mg/Ca and alkenone thermometers with planktonic and benthic foraminiferal δ18O, we determined the phase relationship between local sea surface temperature (SST) and global seawater δ18O changes in the Coral Sea in the Southwestern Pacific over the last 360 ka. The onset of the SST warming preceded the seawater δ18O change by several ka for Termination I, II and III. During Termination I, the SST warming started at 20 ka BP, earlier than atmospheric CO 2 rise suggesting that the greenhouse effect was not the main trigger of this early warming. Compilation of 14C-dated SST records from the whole Pacific during Termination I reveals that the onset of the warming is generally earlier in the Southern and the tropical Pacific than in the North Pacific. This spatio-temporal warming pattern suggests linkage between the southern ocean and tropical Pacific. The early tropical warming could provide heat and moisture to the northern high latitudes, modifying radiative balance and precipitation over ice sheets at the onset of deglaciation.
The magnetic and geochemical properties of four marine sediment cores from the North-Western Amer... more The magnetic and geochemical properties of four marine sediment cores from the North-Western American margin allowed reconstructing the dynamics of the terrigenous sedimentation, related to climatic changes during the last glacial-interglacial cycle (0-120,000 yrs). The cores have been retrieved in three sites located on the Californian and Mexican coasts: Santa Barbara Basin (35°N), margin of Baja California (23°N) and Gulf of Tehuantepec (15°N). The present sedimentation is characterized by high terrigenous input, deposited under the influence of a strong seasonal variability and high accumulation rates (35 to 150 cm/ka), allowing to monitor the rhythms of the terrigenous input at high resolution. The magnetic parameters (magnetic susceptibility, natural, anhysteretic and isothermal remanent magnetizations and hysteresis properties) are used to trace the concentration, nature or grain sizes changes of the magnetic fraction. The type of terrigenous iron oxides and grain sizes identified (magnetite, hematite, goethite) can be related to fluvial or aeolian inputs, and thus to erosion regimes forced by climatic conditions. The relative contents of major and trace elements, measured by X-ray fluorescence scanner (XRF) on key interval of the cores, helped to improve interpretations. The sedimentary sequences, dated by correlation of magnetic susceptibility profiles, calibrated 14C ages and identification of paleomagnetic excursions, totally or partly cover the last glacial-interglacial cycle (0-120 ka). The high concentration of iron oxides in glacial sediments in the three sites suggests strong terrigenous inputs on the NW American margin and notably intense aeolian inputs during the last glacial maximum (20-26 ka BP), revealing a strong erosion in arid conditions affecting wider areas of coastal surfaces (lower sea level). In the Santa Barbara Basin, terrigenous input variations during the last 35 ka were probably modulated by the oscillation of the volume and spatial extension of the North American (Laurentide) Ice cap. The sedimentary sequence off Southern Baja California peninsula covers the last 120 ka and reveals that the fluvial inputs are related to climatic variability of North Atlantic whilst the aeolian inputs are driven by the shifts of the low pressure cells belonging to the North Mexican Monsoon, under direct control of the summer insolation at 23°N. In the Gulf of Tehuantepec, aeolian and fluvial inputs are synchronous over the last 40 ka and may be modulated by both the Trade winds intensity and precipitation regimes.
The western Pacific warm pool (WPWP) is an important heat source for the atmospheric circulation ... more The western Pacific warm pool (WPWP) is an important heat source for the atmospheric circulation and influences climate conditions worldwide. Estimating WPWP sensitivity to past radiative forcing perturbations is important for understanding the magnitudes and patterns of current and projected tropical climate change. Here we present a new Mg/Ca-based sea surface temperature (SST) reconstruction over the past 400 ka from the Bismarck Sea, off Papua New Guinea, along with benthic foraminiferal d 18 O records and a transient intermediate complexity earth system model simulation. The Mg/Ca-SST record exhibits a close similarity with atmospheric CO 2 content for the whole study period. Our model analysis demonstrates that greenhouse gas forcing is the primary driver for glacial/interglacial SST changes in the entire WPWP region. Mg/Ca-SST in the Bismarck Sea also includes a weaker precessional component, which covaries with reconstructed and simulated local precipitation, and simulated surface currents. We propose that orbitally driven latitudinal shifts of the Intertropical Convergence Zone and oceanic heat advection are responsible for this residual SST variability. On glacial timescales the reconstructed WPWP surface temperature changes over the past 400 ka are highly correlated with East Antarctic air temperature variations. The strong effect of greenhouse gas forcings on both records and on global mean temperature variability allows us to determine a scaling factor of 1e1.5 between reconstructed WPWP temperature anomalies and estimates of the global mean temperature.
ABSTRACT Change in past global surface temperature (ΔT) in relation to radiative forcing provides... more ABSTRACT Change in past global surface temperature (ΔT) in relation to radiative forcing provides key information on ongoing global warming. Compilation of extensive paleo-reconstruction and modeling effort have contributed to better constraining ΔT. Another approach is to study in detail specific regions that reflect global signal. Western Pacific Warm Pool (WPWP) is one of the targets since the Sea Surface Temperature (SST) in the WPWP is mainly determined thermodynamically and a tight correlation between tropical SST and global signal is expected. However, highly resolved paleo-SST records have been limited in marginal seas where local effects interfered. Here we present the past 400 kyr SST reconstruction based on planktonic foraminiferal Mg/Ca from a marine sediment in the north of the New Guinea Island, the centre of the present WPWP. Striking similarity and synchronism between the SST, the benthic foraminiferal δ18O of the same core, and the atmospheric CO2 records from Antarctic ice cores indicate that the WPWP SST primarily reflected global signal. A strong linear relationship between the SST and ΔT based on Antarctic temperature further confirms the usefulness of WPWP SST. Obtained SST-based ΔT is coupled with past greenhouse gas and ice sheet albedo forcing to quantify climate sensitivity. This yields 2.4±0.8°C, which agrees well with the recent estimate of 2.3°C. Within uncertainty, glacial and interglacial data give comparable climate sensitivity, suggesting that the impact of climate background would be minor or the current dataset failed to detect the difference because of the large uncertainty.
ABSTRACT Latitudinal movements of the Intertropical Convergence Zone (ITCZ), analogous to its pre... more ABSTRACT Latitudinal movements of the Intertropical Convergence Zone (ITCZ), analogous to its present-day seasonal shifts, and El Niño Southern Oscillation (ENSO)-type interannual variability both potentially impacted the tropical Pacific hydrology during the last glacial period. However, changes in ENSO activity and in the ITCZ dynamics are difficult to disentangle from paleoceanographic reconstructions because they are both embedded in the tropical hydrological signal derived from marine sediment cores. In this presentation we will compare tropical Pacific sedimentary records of paleoprecipitation to decipher which climate mechanism was responsible for the past rainfall changes. We suggest that latitudinal movements of the ITCZ are consistent with the observed rainfall patterns, challenging the ENSO hypothesis for explaining the rapid rainfall changes at low latitudes. The ITCZ-related mechanism appears to reflect large-scale atmospheric rearrangements over the tropical belt, with a pronounced Heinrich-Dansgaard/Oeschger signature. This observation is coherent with the simulated tropical rainfall anomalies induced by a weakening of the Atlantic thermohaline circulation in modeling experiments. This result further implies that changes in ENSO variability are difficult to extract from paleoceanographic reconstructions because they are superimposed on changes in seasonal variability that modulate the first-order climate signal. We circumvent this difficulty by reconstructing thermocline structure from a key sediment core retrieved from the eastern equatorial Pacific. At the core location, changes in hydrologic parameters within the thermocline are linked to ENSO activity, with a reduced influence of seasonal variability compared to surface waters. We performed repeated isotopic analyses (d18O) on single specimens of the thermocline-dwelling planktonic foraminifera Neogloboquadrina dutertrei at several targeted time periods over the last 50 ka to extract the total thermocline variance, a parameter supposed to reveal changes in ENSO. No fundamental changes in amplitude and frequency of the events were detected despite differences in climatic background. However, our data suggest that long-term variations at the thermocline occurred over the last 50 ka, with the highest and lowest ENSO activities occurring during the last glacial period and the Last Glacial Maximum, respectively.
The Levant, influenced by both the Mediterranean Sea and the Saharan–Arabian deserts, is a key re... more The Levant, influenced by both the Mediterranean Sea and the Saharan–Arabian deserts, is a key region for understanding climatic changes in response to glacial/interglacial boundary conditions that have greatly affected regional hydrology. Here, we present the first long-term paleoenvironmental record from the northern Levant, presently much wetter than the southern Levant. Our record derives from the multi-proxy study of a
Holocene Eastern Mediterranean Sea sediments contain an organic-rich sapropel S1 layer that was f... more Holocene Eastern Mediterranean Sea sediments contain an organic-rich sapropel S1 layer that was formed in oxygen-depleted waters. The spatial distribution of this layer revealed that during S1 deposition deep waters were permanently anoxic below 1800 m in water depth. To provide further insight into past Eastern Mediterranean Sea circulation, a multi-proxy approach was applied to a core retrieved close to the 1800 m boundary (at 1780 m). We measured the bulk sediment elemental composition, the stable isotopic composition of the planktonic foraminifer <i>Globigerinoides ruber</i>, and the abundance of benthic foraminifera since the last deglaciation. The result indicates that authigenic U and Mo accumulation began around 13–12 cal ka BP, in concert with surface water freshening estimated from the <i>G. ruber</i> δ<sup>18</sup>O record. The onset of bottom/pore water oxygen depletion occurred prior to S1 deposition inferred from barium enrichment. I...
The low-latitude hydrological cycle is a key climate parameter on different timescales, as it con... more The low-latitude hydrological cycle is a key climate parameter on different timescales, as it contributes to various feedback processes. Modelling studies suggest that the interhemispheric insolation contrast is the major factor controlling the cycle, although the influence of glacial conditions and the phase relationships relative to insolation forcing remain undetermined. In this work, we studied precipitation variability over Papua New Guinea (PNG, 3 S) for the past 400 ka using terrigenous fractions transported by the Sepik River to the Western Pacific Warm Pool (WPWP). A multi-decadal to centennial resolution of the elemental content was obtained using X-ray fluorescence scanning of a marine sediment core using an age model based on 14 C dates and benthic foraminiferal d 18 O. Indicators of the coarse river particulate fraction (bulk and CaCO 3 -free basis Ti concentrations, the log intensity ratios of Ti/K and Ti/Ca) displayed a dominant 23 ka periodicity without a clear glacialeinterglacial trend. Our precipitation records showed a tight relationship with local summer insolation (3 S, January) with time-dependent lag of 0 to 4 ka.
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Papers by Laurence Vidal