Interdecadal variation in the extent of South Pacific tropical waters during the Younger Dryas event

Abstract

been described for the present day 26 and the mid-Holocene 27. Coupled Sr/Ca and d 18 O analyses at biannual and monthly resolution on the YD Diploastrea permit us to derive information about the coupled ocean-atmosphere response to YD cooling indicated by changes in the balance of evaporation and precipitation (Figs 2 and 3). When the relative contributions of SST and changes in d 18 O SW to the coral d 18 O record are deconvolved 24,25 , we find that d 18 O SW tracks SST variability. Although the error on the reconstructed d 18 O SW is large because it includes errors in both the Sr/Ca and d 18 O methods 25 , the main variations in d 18 O SW are robust features of the record. Positive correlation between SST and d 18 O SW is evident on both interdecadal (Fig. 2) and seasonal (Fig. 3) timescales. In the modern tropical western Pacific Ocean, d 18 O SW is positively correlated with sea surface salinity (SSS) 28 , in large part owing to seasonal differences in the amount of 18 O-depleted precipitation. At Vanuatu today, both d 18 O SW and SSS decrease as SST rises during the austral summer intensification of the South Pacific convergence zone (SPCZ), which brings greater in-mixing of 18 O-depleted precipitation. This contrasts with the subtropical southwestern Pacific, where modern coral reconstructions and instrumental records from areas not affected by moisture transport into the SPCZ demonstrate that SST and SSS are positively correlated 24,25. Therefore, in subtropical oceanic settings where evaporation strongly exceeds precipitation, as SST increases, so do d 18 O SW and SSS. This situation is the same as that encountered at Vanuatu during the YD, but opposite to that found today. Given the apparent compression of the tropics towards the Equator during the YD, the positive coupling between SST and d 18 O SW in the Diploastrea record strongly suggests that the SPCZ did not exist during this period. A partial analogue for the YD climate scenario is provided by modern El Niño events, when the Western Pacific warm pool contracts towards the Equator and the SPCZ migrates northwards to merge with the inter-tropical convergence zone. It is beyond the scope of the present study to determine the potential mechanisms for the strong interdecadal variability during the YD documented by the Diploastrea record. Although recent modelling studies 29,30 indicate that interdecadal variability in the tropical Pacific can be generated solely by tropical wind forcing, most theories invoke links to the mid-latitudes. Clearly, more high-resolution palaeoclimate records from low to high latitudes, and further modelling studies, are needed to fully understand the ocean-atmosphere processes driving the altered YD climatic regime. A

Pronounced interannual variability in tropical South Pacific temperatures during Heinrich Stadial 1

“…S9). The Sr/Ca ratios in coral skeletons are an established proxy for SST variability 10,11,[25][26][27][28] . Here we present a monthly resolved Sr/Ca-based SST reconstruction for a time window of 22 years generated from our HS1 coral (Fig.…”

“…In contrast, seasonally resolved records from fossil shallow-water corals were successfully used to reconstruct interannual ENSO variability in the tropical Pacific during the last glacial 9 , but represent short intervals older than 38,000 years only. A few coral records are available for intervals of the last glacial termination [10][11][12][13][14] , but are too short to document significant interannual ENSO variability. In modern observations, ENSO variability is described by monitoring tropical Pacific sea surface temperature (SST) 15 .…”

Past daily light cycle recorded in the strontium/calcium ratios of giant clam shells

“…This work presented new measurements of Sr/Ca, Mg/Ca and Ba/Ca in the finest temporal resolution to date in the carbonate geochemistry literature [1][2][3][4][5][6][7][8][9] . Although there is some ambiguity in the age model, the giant clam Sr/Ca data clearly demonstrated the daily light cycle, which we attributed to insolation-driven, differential rates of growth and calcification.…”

“…Thus, biogenic marine carbonates are important tools for reconstruction of the past climate system. Proxies reflecting past seawater temperature [1][2][3] , salinity 4,5 , pH 6,7 , and nutrients 8,9 has been derived from stable isotopes and trace elements in coral skeletons, foraminifera tests, and mollusk shells. Insolation is an important component of meteorological data, as solar energy is the primal and direct driver of weather and climate.…”

Modern and Pleistocene Reservoir Ages Inferred from South Pacific Corals

“…An intriguing feature of our record are large reservoir age increases that just precede growth hiatuses, suggesting a concomitant decrease in water temperature ( Figure 5). We know from trace element studies of this same coral that the average sea surface temperature (SST) at the time was 4.5 °C cooler than today, and that this was accompanied by substantial SST variability (Corrège et al 2004). It is also observed that the coral only recovered from the growth hiatus after the reservoir age dropped to lower values.…”