Southern Hemisphere climate variability forced by Northern Hemisphere ice-sheet topography

The presence of large Northern Hemisphere ice sheets and reduced greenhouse gas concentrations during the Last Glacial Maximum fundamentally altered global ocean–atmosphere climate dynamics1. Model simulations and palaeoclimate records suggest that glacial boundary conditions affected the El Niño–Southern Oscillation2,3, a dominant source of short-term global climate variability. Yet little is known about changes in short-term climate variability at mid- to high latitudes. Here we use a high-resolution water isotope record from West Antarctica to demonstrate that interannual to decadal climate variability at high southern latitudes was almost twice as large at the Last Glacial Maximum as during the ensuing Holocene epoch (the past 11,700 years). Climate model simulations indicate that this increased variability reflects an increase in the teleconnection strength between the tropical Pacific and West Antarctica, owing to a shift in the mean location of tropical convection. This shift, in turn, can be attributed to the influence of topography and albedo of the North American ice sheets on atmospheric circulation. As the planet deglaciated, the largest and most abrupt decline in teleconnection strength occurred between approximately 16,000 years and 15,000 years ago, followed by a slower decline into the early Holocene

The effect of ocean alkalinity and carbon transfer on deep-sea carbonate ion concentration during the past five glacial cycles

Glacial–interglacial deep Indo-Pacific carbonate ion concentration ([CO32−]) changes were mainly driven by two mechanisms that operated on different timescales: 1) a long-term increase during glaciation caused by a carbonate deposition reduction on shelves (i.e., the coral reef hypothesis), and 2) transient carbonate compensation responses to deep ocean carbon storage changes. To investigate these mechanisms, we have used benthic foraminiferal B/Ca to reconstruct deep-water [CO32−] in cores from the deep Indian and Equatorial Pacific Oceans during the past five glacial cycles. Based on our reconstructions, we suggest that the shelf-to-basin shift of carbonate deposition raised deep-water [CO32−], on average, by 7.3 ± 0.5 (SE) μmol/kg during glaciations. Oceanic carbon reorganisations during major climatic transitions caused deep-water [CO32−] deviations away from the long-term trend, and carbonate compensation processes subsequently acted to restore the ocean carbonate system to new steady state conditions. Deep-water [CO32−] showed similar patterns to sediment carbonate content (%CaCO3) records on glacial–interglacial timescales, suggesting that past seafloor %CaCO3 variations were dominated by deep-water carbonate preservation changes at our studied sites

The effect of ocean alkalinity and carbon transfer on deep-sea carbonate ion concentration during the past five glacial cycles

Glacial–interglacial deep Indo-Pacific carbonate ion concentration ([CO32−]) changes were mainly driven by two mechanisms that operated on different timescales: 1) a long-term increase during glaciation caused by a carbonate deposition reduction on shelves (i.e., the coral reef hypothesis), and 2) transient carbonate compensation responses to deep ocean carbon storage changes. To investigate these mechanisms, we have used benthic foraminiferal B/Ca to reconstruct deep-water [CO32−] in cores from the deep Indian and Equatorial Pacific Oceans during the past five glacial cycles. Based on our reconstructions, we suggest that the shelf-to-basin shift of carbonate deposition raised deep-water [CO32−], on average, by 7.3 ± 0.5 (SE) μmol/kg during glaciations. Oceanic carbon reorganisations during major climatic transitions caused deep-water [CO32−] deviations away from the long-term trend, and carbonate compensation processes subsequently acted to restore the ocean carbonate system to new steady state conditions. Deep-water [CO32−] showed similar patterns to sediment carbonate content (%CaCO3) records on glacial–interglacial timescales, suggesting that past seafloor %CaCO3 variations were dominated by deep-water carbonate preservation changes at our studied sites

LAtools: A data analysis package for the reproducible reduction of LA-ICPMS data

Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) is an increasingly popular analytical technique, that is able to provide spatially resolved, minimally destructive analyses of heterogeneous materials. The data produced by this technique are inherently complex, and require extensive processing and subjective expert interpretation to produce useful compositional data. At present, laboratories employ diverse protocols for data processing, and the reporting of these protocols is usually insufficient to allow data processing to be independently replicated, rendering the resulting data untraceable. Importantly, different expert users can obtain significantly different results from the same raw data using nominally identical processing workflows, depending on how ‘contaminants’ are identified and excluded, and which regions of signal are selected as representative of the composition of the sample. The irreproducibility of LA-ICPMS is a significant problem for the technique, but the complexity of the raw data has been a major hindrance to developing traceable data processing workflows. Here, we present LAtools – a free, open-source Python package for LA-ICPMS data processing designed with reproducibility at its core. The software performs basic data processing with similar efficacy to existing software, and brings a number of new data selection algorithms to facilitate reproducible reduction of LA-ICPMS data. We discuss the key advances of LAtools, and compare its output to trace metal analysis of marine CaCO3 (foraminifera) processed both manually and with Iolite, and to manually processed trace element data from zircon grains