[1] The Sr/Ca ratio of coral aragonite is used to reconstruct past sea surface temperature (SST). Twentyone laboratories took part in an interlaboratory study of coral Sr/Ca measurements. Results show interlaboratory bias can be significant, and in the extreme case could result in a range in SST estimates of 7 C. However, most of the data fall within a narrower range and the Porites coral reference material JCp-1 is now characterized well enough to have a certified Sr/Ca value of 8.838 mmol/mol with an expanded uncertainty of 0.089 mmol/mol following International Association of Geoanalysts (IAG) guidelines. This uncertainty, at the 95% confidence level, equates to 1.5 C for SST estimates using Porites, so is approaching fitness for purpose. The comparable median within laboratory error is <0.5 C. This difference in uncertainties illustrates the interlaboratory bias component that should be reduced through the use of reference materials like the JCp-1. There are many potential sources contributing to biases in comparative methods but traces of Sr in Ca standards and uncertainties in reference solution composition can account for half of the combined uncertainty. Consensus values that fulfil the requirements to be certified values were also obtained for Mg/Ca in JCp-1 and for Sr/Ca and Mg/Ca ratios in the JCt-1 giant clam reference material. Reference values with variable fitness for purpose have also been obtained for Li/Ca, B/Ca, Ba/Ca, and U/Ca in both reference materials. In future, studies reporting coral element/Ca data should also report the average value obtained for a reference material such as the JCp-1.

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

Abstract. We present a 47-year-long record of sea surface temperature (SST) derived from St/Ca and U/Ca analysis of a massive Potires coral which grew at-4150 calendar years before present (B.P.) in Vanuatu (southwest tropical Pacific Ocean). Mean SST is similar in both the modern instrumental record and paleorecord, and both exhibit E1 NifioSouthern Oscillation (ENSO) frequency SST oscillations. However, several strong decadal-frequency cooling events and a marked modulation of the seasonal SST cycle, with power at both ENSO and decadal frequencies, are observed in the paleorecord, which are unprecedented in the modern record.

The natural river water certified reference material SLRS‐4 (NRC‐CNRC, National Research Council‐Conseil National de Recherches Canada) has been routinely analysed for major and trace elements by six French laboratories. Most measurements were made using inductively coupled plasma‐mass spectrometry. For silicon and thirty one trace elements (rare earth elements, Ag, B, Br, Cs, Ga, Ge, Li, P, Pd, Rb, Se, Th, Ti, Tl, W, Y and Zr), no certified values are assigned by NRC‐CNRC. We propose some compilation values and related uncertainties according to the results obtained by the different laboratories.

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Increasing atmospheric CO2 from man-made climate change is reducing surface ocean pH. Due to limited instrumental measurements and historical pH records in the world’s oceans, seawater pH variability at the decadal and centennial scale remains largely unknown and requires documentation. Here we present evidence of striking secular trends of decreasing pH since the late nineteenth century with pronounced interannual to decadal–interdecadal pH variability in the South Pacific Ocean from 1689 to 2011 CE. High-amplitude oceanic pH changes, likely related to atmospheric CO2 uptake and seawater dissolved inorganic carbon fluctuations, reveal a coupled relationship to sea surface temperature variations and highlight the marked influence of El Niño/Southern Oscillation and Interdecadal Pacific Oscillation. We suggest changing surface winds strength and zonal advection processes as the main drivers responsible for regional pH variability up to 1881 CE, followed by the prominent role of anthropogenic CO2 in accelerating the process of ocean acidification.

International audienceWe present early mid-Holocene records of Sr/Ca, δ¹⁸O and δ¹⁸O_sw from marine archives collected in Vanuatu: two Porites sp. corals (6.7-6.5 ka BP) and a Tridacna maxima giant clam (6.2-6.0 ka BP). Sr/Ca, δ¹⁸O, and δ¹⁸O_sw were used as proxies for sea surface temperature (SST) and sea surface salinity (SSS). The fossil geochemical records were compared to modern Porites sp. and T. maxima records. Reconstructed mean SSTs from the two fossil Porites sp. and from the modern coral are similar, implying that the Western Pacific Warm Pool (WPWP)' southern edge had reached its modern location by 6.7-6.5 ka BP. The post-glacial SST rise in the Southwest Pacific was thus completed by the early mid-Holocene. The two early mid-Holocene corals and the giant clam recorded saltier conditions than modern related to 1) a decoupling between the precipitation regime and the SPCZ due to a northerly position of this climatic feature and 2) an increase of the moisture transport to the extra-tropics, driven by a strengthened or extended Hadley cell. The longest δ¹⁸O coral profile displays an El Niño Southern Oscillation (ENSO) signal reduced by 20-30% compared to the period 1928-1992, in concordance with the reduced ENSO variability observed in the Pacific area during the first half of the Holocene. However, the decoupling between the SPCZ and the precipitation regime may have also contributed to the weak ENSO signal recorded in the early mid-Holocene coral δ¹⁸O profile