Assessment of sea surface temperature changes in the Gulf of Cadiz during the last 30 ka: implications for glacial changes in the regional hydrography

Abstract. New dinocyst analyses were conducted on core MD99-2339 retrieved from the central Gulf of Cadiz. Dinocyst and foraminiferal assemblages from this core are combined with existing data off SW Portugal and NW Morocco to investigate past hydrological and primary productivity regimes in the subtropical NE Atlantic Ocean over the last 30 ka. Our results have revealed highest upwelling intensity during Heinrich Stadial 1 (HS 1) and the Younger Dryas and weaker upwelling cells during the Last Glacial Maximum (LGM) and HS 2, off the SW Iberian and NW Moroccan margins. Similar assemblages between the Gulf of Cadiz and the NW Moroccan margin, and distinct species off Portugal, were observed during the cold climatic extremes that punctuated the last 30 ka. This pattern has been linked to the occurrence of a hydrological structure between SW Iberia and Cadiz during the last glacial period, perhaps similar to the modern Azores Front. This front was probably responsible locally for heterotrophic dinocysts found in the Gulf of Cadiz during the last glacial period, even if this sector is not conductive to upwelling phenomena by Ekman transport. Regional reconstructions of paleo-sea-surface temperatures (SSTs) using dinocyst and foraminiferal transfer functions, as well as alkenones, are also discussed and depict coherent scenarios over the last 30 ka. Seasonal reconstructions of LGM SSTs obtained with this multi-proxy panel are discussed jointly with model outputs in order to contribute to ongoing efforts in model-data comparison.

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Hydrological processes affecting the subtropical NE Atlantic (34–38° N) over the last 30 ka: evidence from phyto- and zooplankton assemblages

Biogeosciences Discussions ◽

10.5194/bgd-8-2281-2011 ◽

2011 ◽

Vol 8 (2) ◽

pp. 2281-2327 ◽

Cited By ~ 2

Author(s):

A. Penaud ◽

F. Eynaud ◽

A. Voelker ◽

F. Marret ◽

J. L. Turon ◽

...

Keyword(s):

Transfer Functions ◽

Distinct Species ◽

Ekman Transport ◽

Glacial Period ◽

Gulf Of Cadiz ◽

Ne Atlantic ◽

Last Glacial Period ◽

Last Glacial ◽

Gulf Of Cádiz ◽

The Last Glacial

Abstract. New dinocyst analyses were conducted on core MD99-2339 retrieved from the central Gulf of Cadiz. Dinocyst and foraminiferal assemblages from this core are combined with existing data off SW Portugal and NW Morocco to investigate past hydrological and primary productivity regimes in the subtropical NE Atlantic Ocean over the last 30 ka. Our results have revealed highest upwelling intensity during Heinrich Stadial 1 (HS 1) and the Younger Dryas and weaker upwelling cells during the Last Glacial Maximum and HS 2, off the SW Iberian and NW Moroccan margins. Similar assemblages between Cadiz and Morocco and distinct species off Portugal were observed during the cold climatic extremes that punctuated the last 30 ka. This pattern has been linked to the occurrence of a hydrological structure between SW Iberia and Cadiz during the last glacial period, probably similar to the modern Azores Front. This front was probably responsible locally for heterotrophic dinocysts found in the Gulf of Cadiz during the last glacial period, even if this sector is not conductive to upwelling phenomena by Ekman transport. Regional reconstructions of paleo-sea-surface temperatures using dinocyst and foraminiferal transfer functions, as well as alkenones, are also discussed and depict coherent scenarios over the last 30 ka. However, some mismatches are observed between the different quantitative reconstructions such as during HS 1 in the Gulf of Cadiz and during the LGM at the three core locations.

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TROPICAL SEA-SURFACE TEMPERATURES DURING THE LAST GLACIAL PERIOD: A VIEW BASED ON ALKENONES IN INDIAN OCEAN SEDIMENTS

Quaternary Science Reviews ◽

10.1016/s0277-3791(97)00099-1 ◽

1998 ◽

Vol 17 (12) ◽

pp. 1185-1201 ◽

Cited By ~ 136

Author(s):

CORINNE SONZOGNI ◽

EDOUARD BARD ◽

FRAUKE ROSTEK

Keyword(s):

Indian Ocean ◽

Sea Surface ◽

Sea Surface Temperatures ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

Surface Temperatures ◽

Tropical Sea ◽

The Last Glacial

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Abrupt sea surface pH change at the end of the Younger Dryas in the central sub-equatorial Pacific inferred from boron isotope abundance in corals (<i>Porites</i>)

Biogeosciences Discussions ◽

10.5194/bgd-7-1959-2010 ◽

2010 ◽

Vol 7 (2) ◽

pp. 1959-1993 ◽

Cited By ~ 5

Author(s):

E. Douville ◽

M. Paterne ◽

G. Cabioch ◽

P. Louvat ◽

J. Gaillardet ◽

...

Keyword(s):

Younger Dryas ◽

Equatorial Pacific ◽

Sea Surface ◽

Glacial Period ◽

Ph Change ◽

Last Glacial Period ◽

Surface Ph ◽

The Holocene ◽

Last Glacial ◽

The Last Glacial

Abstract. The "δ11B-pH" technique was applied to modern and ancient Porites from the sub-equatorial Pacific areas (Tahiti and Marquesas) spanning a time interval from 0 to 20 720 calendar years to determine the amplitude of pH changes between the Last Glacial Period and the Holocene. Boron isotopes were measured by Multi-Collector-Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) with an external reproducibility of 0.25‰, allowing a precision of ±0.025 pH-units. The boron concentration [B] and isotopic composition of modern samples indicate that the temperature strongly controls the partition coefficient KD for different aragonite species. Modern coral δ11B values and the reconstructed sea surface pH values for different Pacific areas match the measured pH expressed on the Sea Water Scale and confirm the calculation parameters that were previously determined by laboratory calibration exercises. Most ancient sea surface pH reconstructions near Marquesas are higher than modern values. These values range between 8.20 and 8.26 for the Holocene and reached 8.31 at the end of the last glacial period (20.7 kyr BP). At the end of the Younger Dryas (11.50±0.1 kyr BP), the central sub-equatorial Pacific experienced a dramatic drop of up to 0.2 pH-units from the average pH of 8.2 before and after this short event. Using the CO2SYS program, we recalculated the aqueous pCO2 to be 400±24 ppmV at around 11.5 kyr BP for corals at Marquesas and ~500 ppmV near Tahiti where it was assumed that pCO2 in the atmosphere was 250 ppmV. Throughout the Holocene, the difference in pCO2 between the ocean and the atmosphere at Marquesas (ΔpCO2) indicates that the surface waters behave as a moderate CO2 sink (−67 to −11 ppmV) during El Niño-like conditions. In contrast, during the last glacial/interglacial transition, this area was a moderate source of CO2 (−9 to 56 ppmV) for the atmosphere, highlighting predominant La Niña-like conditions. Such conditions were particularly pronounced at the end of the Younger Dryas with a large amount of CO2 released with ΔpCO2 of +140 ppmV. This last finding provides further evidence of the marked changes to the water mass pH and temperature properties in the equatorial Pacific at the Younger Dryas- Holocene transition and the strong impact of oceanic dynamic on the atmospheric CO2 content.

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Abrupt sea surface pH change at the end of the Younger Dryas in the central sub-equatorial Pacific inferred from boron isotope abundance in corals (<i>Porites</i>)

Biogeosciences ◽

10.5194/bg-7-2445-2010 ◽

2010 ◽

Vol 7 (8) ◽

pp. 2445-2459 ◽

Cited By ~ 44

Author(s):

E. Douville ◽

M. Paterne ◽

G. Cabioch ◽

P. Louvat ◽

J. Gaillardet ◽

...

Keyword(s):

Younger Dryas ◽

Equatorial Pacific ◽

Sea Surface ◽

Glacial Period ◽

Last Glacial Period ◽

Surface Ph ◽

The Holocene ◽

Last Glacial ◽

Ph Values ◽

The Last Glacial

Abstract. The "δ11B-pH" technique was applied to modern and ancient corals Porites from the sub-equatorial Pacific areas (Tahiti and Marquesas) spanning a time interval from 0 to 20.720 calendar years to determine the amplitude of pH changes between the Last Glacial Period and the Holocene. Boron isotopes were measured by Multi-Collector – Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) with an external reproducibility of 0.25‰, allowing a precision of about ±0.03 pH-units for pH values between 8 and 8.3. The boron concentration [B] and isotopic composition of modern samples indicate that the temperature strongly controls the partition coefficient KD for different aragonite species. Modern coral δ11B values and the reconstructed sea surface pH values for different Pacific areas match the measured pH expressed on the seawater scale and confirm the calculation parameters that were previously determined by laboratory calibration exercises. Most ancient sea surface pH reconstructions near Marquesas are higher than modern values. These values range between 8.19 and 8.27 for the Holocene and reached 8.30 at the end of the last glacial period (20.7 kyr BP). At the end of the Younger Dryas (11.50±0.1 kyr BP), the central sub-equatorial Pacific experienced a dramatic drop of up to 0.2 pH-units from the average pH of 8.2 before and after this short event. Using the marine carbonate algorithms, we recalculated the aqueous pCO2 to be 440±25 ppmV at around 11.5 kyr BP for corals at Marquesas and ~500 ppmV near Tahiti where it was assumed that pCO2 in the atmosphere was 250 ppmV. Throughout the Holocene, the difference in pCO2 between the ocean and the atmosphere at Marquesas (ΔpCO2) indicates that the surface waters behave as a moderate CO2 sink or source (−53 to 20 ppmV) during El Niño-like conditions. By contrast, during the last glacial/interglacial transition, this area was a marked source of CO2 (21 to 92 ppmV) for the atmosphere, highlighting predominant La Niña-like conditions. Such conditions were particularly pronounced at the end of the Younger Dryas with a large amount of CO2 released with ΔpCO2 of +185±25 ppmV. This last finding provides further evidence of the marked changes in the surface water pH and temperature in the equatorial Pacific at the Younger Dryas-Holocene transition and the strong impact of oceanic dynamic on the atmospheric CO2 content.

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