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>)

The "δ¹¹B-pH" technique was applied to modern and ancient corals <i>Porites</i> 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&permil;, allowing a precision of about &plusmn;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 K_<i>D</i> 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&plusmn;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 <i>p</i>CO₂ to be 440&plusmn;25 ppmV at around 11.5 kyr BP for corals at Marquesas and ~500 ppmV near Tahiti where it was assumed that <i>p</i>CO₂ in the atmosphere was 250 ppmV. Throughout the Holocene, the difference in <i>p</i>CO₂ between the ocean and the atmosphere at Marquesas (Δ<i>p</i>CO₂) 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 Δ<i>p</i>CO₂ of +185&plusmn;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

Madagascar corals track sea surface temperature variability in the Agulhas Current core region over the past 334 years

The Agulhas Current (AC) is the strongest western boundary current in the Southern Hemisphere and is key for weather and climate patterns, both regionally and globally. Its heat transfer into both the midlatitude South Indian Ocean and South Atlantic is of global significance. A new composite coral record (Ifaty and Tulear massive Porites corals), is linked to historical AC sea surface temperature (SST) instrumental data, showing robust correlations. The composite coral SST data start in 1660 and comprise 200 years more than the AC instrumental record. Numerical modelling exhibits that this new coral derived SST record is representative for the wider core region of the AC. AC SSTs variabilities show distinct cooling through the Little Ice Age and warming during the late 18th, 19th and 20th century, with significant decadal variability superimposed. Furthermore, the AC SSTs are teleconnected with the broad southern Indian and Atlantic Oceans, showing that the AC system is pivotal for inter-ocean heat exchange south of Africa

Light effects on the isotopic fractionation of skeletal oxygen and carbon in the cultured zooxanthellate coral, &lt;i&gt;Acropora&lt;/i&gt;: implications for coral-growth rates

International audienceSkeletal isotopic and metabolic measurements of the branching coral Acropora cultured in constant conditions and subjected to two light intensities were revisited. We individually compared the data recorded at low light (LL) and high light (HL) for 24 colonies, all derived from the same parent colony. Metabolic and isotopic responses to the different light levels were highly variable. High light led to productivity enhancement, reduction of surface extension, doubling of aragonite deposited weight and increased δ 18 O levels in all nubbins; responses in respiration and δ 13 C were not clear. The partitioning of the colonies cultured at HL into two groups, one showing a δ 13 C enrichment and the other a δ 13 C decrease revealed common behaviors. Samples showing an increase in δ 13 C were associated with the co-variation of low surface extension and high productivity while samples showing a decrease in δ 13 C were associated with the co-variation of higher surface extension and limited productivity. This experiment, which allowed for the separation of temperature and light effects on the coral, highlighted the significant light influences on both skeletal δ 18 O and δ 13 C. The high scattering of inter-colony δ 18 O observed at one site could be due to the differing photosynthetic responses of symbiotic algal assemblages. We compared our results with observations by Gladfelter on Acropora cervicornis (1982). Both set of results highlight the relationships between coral-growth rates, micro-structures and photosynthetic activity. It appears that extension growth and skeleton thickening are two separate growth Correspondence to: A. Juillet-Leclerc ([email protected]) modes, and thickening is light-enhanced while extension is light-suppressed. There are multiple consequences of these findings for paleoclimatic reconstructions involving corals

Temperature variability in the Gulf of California during the last century: a record of the recent strong El Nino

International audienceThe oxygen isotopic ratio of diatom silica from a box core collected on the eastern slope of the Guaymas Basin (Gulf of California) has been analyzed. This core covers the last 90 years. The isotopic record indicates a progressive and continuous temperature increase of about 8°C from the end of the last century until 1980 with superimposed, rapid temperature fluctuations of 2 to 4°C. Although the Gulf of California is not directly under the influence of El Niño, short temperature increases may be associated with the El Niño events described by Quinn et al. (1987). The longer term changes are attributed to a decrease of upwelling intensity linked to weakening of the trade winds in the Northern Hemisphere

Modern and last glacial maximum sea surface δ18O derived from an Atmospheric General Circulation Model

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The Measured Coral Oxygen Isotopes Result of The Superimposition of Two Fractionations

International audienceCoral oxygen isotopes (d18O) are regarded as a robust proxy of environmental variables. Despite the apparent isotopic desequilibrium, attributed to a kinetic behavior, there is a strong temperature dependence. The calibrations are usually performed by comparing monthly proxy records of a coral head with instrumental data over the last decades. However the derived temperature variations, even over only the last century, match very poorly with the observed SST record. The geochemical proxies measured from coral skeletons are governed by physical processes strongly influenced by the vital effect. The oxygen isotopes from aragonite record temperature and/or water isotopic composition (d18Osw) changes. The formulas vary according to the species and the local conditions but the isotopic deviation per 1°C is very close to the coefficient inferred for calcite by Urey. This result suggests that the isotopic desequilibrium is the same for a colony during its lifetime. The isotopic desequilibrium affects both oxygen and carbon. By comparing several coral records we demonstrate that interannual oxygen and carbon isotopic curves exhibit a common shape and it is possible to separate the O and C common signal from the measured d18O variations by using EOF analysis. Two modes are generated by the analyses, which are converted into oxygen isotopic composition; the d18O calculated from the first mode is called d18Ocommon whereas the second mode is called d18O residual. We proof that d18O residual, is the thermodynamic isotopic response and d18Ocommon is the modulation of the d18O offset, due to a kinetic process occuring during calcium carbonate deposition. d18O residual obeys to temperature and d18Osw changes. The d18Ocommon variations are temperature and salinity dependent. Since d18Osw and salinity, covary, the relationship which links d18Osw and salinity being specific at each site, d18Ocommon and d18O residual may be expressed following temperature and salinity,. Thus from each coral head it is possible to reconstruct temperature and salinity back in time from oxygen and carbon aragonite isotopes

Intermediate and Deep Water Characteristics during the Last Glacial Maximum

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Seasonal variation of primary productivity and skeletal delta13C and delta18O in the zooxanthellate scleractinian coral Acropora formosa

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Mesures conjointes des rapports Sr/Ca et d18O effectuées sur Acropara nobilis et Porites lutea: le paléothermomètre Sr/Ca est-il toujours fiable ?

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Microanalysis of C and O isotopes of azooxanthellate and zooxanthellate corals by ion microprobe

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