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[1] Quasi-periodic variation in sea-surface temperature, precipitation, and sea-level pressure in the equatorial Pacific known as the El Nino – Southern Oscillation (ENSO) is an important mode of interannual variability in global climate. A collapse of the tropical Pacific onto a state resembling a so-called ‘permanent El Nino’, with a preferentially warmed eastern equatorial Pacific, flatter thermocline, and reduced interannual variability, in a warmer world is predicted by prevailing ENSO theory. If correct, future warming will be accompanied by a shift toward persistent conditions resembling El Nino years today, with major implications for global hydrological cycles and consequent impacts on socioeconomic and ecological systems. However, much uncertainty remains about how interannual variability will be affected. Here, we present multi-annual records of climate derived from growth increment widths in fossil bivalves and co-occurring driftwood from the Antarctic peninsula that demonstrate significant variability in the quasi-biennial and 3–6 year bands consistent with ENSO, despite early Eocene (∼50 Mya) greenhouse conditions with global average temperature ∼10 degrees higher than today. A coupled climate model suggests an ENSO signal and teleconnections to this region during the Eocene, much like today. The presence of ENSO variation during this markedly warmer interval argues for the persistence of robust interannual variability in our future greenhouse world.

Interannual and intra-annual variations in lithium-to-calcium ratio were investigated with high temporal resolution in the aragonitic outer shell layer of juvenile Arctica islandica (Mollusca; Bivalvia) collected alive in 2006 off northeast Iceland. Li/Ca shell ranged between 7.00 and 11.12 µmol mol -1 and presented well-marked seasonal cycles with minimum values recorded at the annual growth lines; a general pattern was a progressive increase in Li/Ca shell from March to May, followed by a plateau in June and a decrease down to minimum values in July-August. Li/Ca shell was correlated with d 18 O shell -derived temperature, but the strength of this relationship was weak ( r 2 p shell in A. islandica may most likely be explained (1) by calcification rate and/or (2) by significant river inputs of Li-rich silicate particles flowing to the sea as soon as snow melts. In the first case, Li/Ca shell may be a useful proxy for addressing seasonal variations of growth rate in bivalves that lack discernable microgrowth patterns. Abrupt decreases of Li/Ca shell may, in turn, help identify growth retardations due to harsh environmental conditions. Alternatively, if Li/Ca shell variations are linked to particulate Li inputs by rivers, this could be a new proxy for the intensity of mechanical weathering of Icelandic basalts, with interesting perspectives for the reconstruction of frequency and intensity of past jokulhlaups (subglacial outburst floods). Further works, including experimental studies, are needed to test these hypotheses.

[1] The creation of networks of shell-based chronologies which can provide regionally extensive high-resolution proxies for the marine environment depends on the spatial extent of the common environmental signal preserved in the shell banding and on the reliability of the dating model. Here Arctica islandica chronologies from five neighboring sites in the North Sea are compared, and the strength of the common environmental signal across distances up to 80 km is analyzed using statistical techniques derived from dendrochronology. The signal is found to be coherent across these distances. In a linked study, chronologies based on one of the same sites but constructed by two different research teams are compared. Methodological differences in increment interpretation are found to lead to slippage in the dating models. Systematic inclusion or exclusion of intermittently occurring increments results in the two chronologies becoming misaligned by 4 years over a 70-year period. Comparisons with neighboring chronologies indicate that such increments can generally be regarded as genuine annual increments even if they are not visible in all shells.

[1] Climate archives contained in shells of the European limpet, Patella vulgata, accumulated in archaeological deposits can potentially provide much needed information about Holocene environmental change in midlatitude coastal areas. Before reconstructing climate information preserved in these zooarchaeological records, we studied the controls on oxygen and carbon isotope ratios (δ18O and δ13C, respectively) in modern specimens. We tested the hypothesis that P. vulgata precipitates its shell in isotopic equilibrium with the ambient water by comparing δ18OSHELL with predicted values. Predicted δ18OSHELL was constructed using observed sea surface temperature (SST) records and the equilibrium fractionation equation for calcite and water. We assumed a constant δ18OWATER value of +0.10‰ (VSMOW) based on published regional measurements. Comparison of δ18OSHELL with predicted values revealed that δ18OSHELL values were higher than expected by +1.01 ± 0.21‰. Consequently, estimated SST calculated from δ18OSHELL was 4.2 ± 2.3°C lower than observed SST. However, because of the relatively uniform offset between observed and expected δ18O, an adjustment can be made to account for this predictable vital effect. Thus past climate can be reliably reconstructed using this temperature proxy once the offset is taken into account. δ13C values have a similar cyclicity to the δ18O variation and therefore vary seasonally. However, δ13C is slightly out of phase relative to δ18O. An overall negative shift in δ13CSHELL over the lifetime of the individual indicates a vital effect associated with ontogeny. Further study of environmental and ecological factors that influence shell δ13C is required to evaluate fully the potential of carbon isotope ratios as a useful environmental proxy.

[1] While recent changes in subarctic North Pacific climate had dramatic effects on ecosystems and fishery yields, past climate dynamics and teleconnection patterns are poorly understood due to the absence of century-long high-resolution marine records. We present the first 117-year long annually resolved marine climate history from the western Bering Sea/Aleutian Island region using information contained in the calcitic skeleton of the long-lived crustose coralline red alga Clathromorphum nereostratum, a previously unused climate archive. The skeletal δ18O-time series indicates significant warming and/or freshening of surface waters after the middle of the 20th century. Furthermore, the time series is spatiotemporally correlated with Pacific Decadal Oscillation (PDO) and tropical El Nino-Southern Oscillation (ENSO) indices. Even though the western Bering Sea/Aleutian Island region is believed to be outside the area of significant marine response to ENSO, we propose that an ENSO signal is transmitted via the Alaskan Stream from the Eastern North Pacific, a region of known ENSO teleconnections.