The Antarctic shelf is traversed by large-scale troughs developed by glacial erosion. Swath bathymetric, lithologic, and chronologic data from jumbo piston cores from four sites along the East Antarctic margin (Iceberg Alley, the Nielsen Basin, the Svenner Channel, and the Mertz-Ninnis Trough) are used to demonstrate that these cross-shelf features controlled development of calving bay reentrants in the Antarctic ice sheet during deglaciation. At all sites except the Mertz-Ninnis Trough, the transition between the Last Glacial Maximum and the Holocene is characterized by varved couplets deposited during a short interval of extremely high primary productivity in a fjordlike setting. Nearly monospecific layers of the diatom Chaetoceros alternate with slightly more terrigenous layers containing a mixed diatom assemblage. We propose that springtime diatom blooms dominated by Chaetoceros were generated within well-stratified and restricted surface waters of calving bays that were influenced by the input of iron-rich meltwater. Intervening post-bloom summer-fall laminae were formed through the downward flux of terrigenous material sourced from melting glacial ice combined with mixed diatom assemblages. Radiocarbon-based chronologies that constrain the timing of deposition of the varved sediments within calving bay reentrants along the East Antarctic margin place deglaciation between ca. 10,500-11,500 cal yr B.P., postdating Meltwater Pulse 1A (14,200 cal yr B.P.

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Observations on the relationship between the Antarctic coastal diatoms Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen and sea ice concentrations during the Late Quaternary, Marine Micropaleontology (2009Micropaleontology ( ), doi: 10.1016Micropaleontology ( /j.marmicro.2009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTThe available ecological and palaeoecological information for two sea ice-related marine diatoms 35 (Bacillariophyceae), Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen, 36 suggests that these two species have similar sea surface temperature (SST), sea surface salinity 37 (SSS) and sea ice proximity preferences. From phytoplankton observations, both are described as 38 summer or autumn bloom species, commonly found in low SST waters associated with sea ice, 39 although rarely within the ice. Both species form resting spores (RS) as irradiance decreases, SST 40 falls and SSS increases in response to freezing ice in autumn. Recent work analysing late 41Quaternary seasonally-laminated diatom ooze from coastal Antarctic sites has revealed that sub- that used a coupled atmosphere-sea ice-vegation model forced with orbital parameters and 57 greenhouse gas concentrations. We find that abundance of P. glacialis RS is favoured by higher 58 A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT4 winter and spring sea ice concentrations and that a climatically-sensitive threshold exists between 59 the abundance of P. glacialis RS and T. antarctica RS in the sediments. An increase to >0.1 for the 60 ratio of P. glacialis RS:T. antarctica RS indicates a change to increased winter sea ice 61 concentration (to >80% concentration), cooler spring seasons with increased sea ice, slightly 62 warmer autumn seasons with less sea ice and a change from ~7.5 months annual sea ice cover at a 63 site to much greater than 7.5 months. In the East Antarctic sediment record, an increase in the ratio 64 from <0.1 to above 0.1 occurs at the transition from the warmer Hypsithermal climate into the 65 cooler Neoglacial climate (~4 cal kyr) indicating that the ratio between these two diatoms has the 66 potential to be used as a semi-quantitative climate proxy. antarctica RS-dominated sub-laminae that were deposited during autumn (Stickley et al., 2005). antarctica RS and P. glacialis RS sub-laminae from both sites, and from both time intervals, occur 88 at the top of late summer/autumn terrigenous-rich diatom laminae, which supports the contention 89 that these two diatoms have broadly similar ecological pre...

The Antarctic Peninsula is one of the most sensitive regions of Antarctica to climate change. Here, ecological and cryospheric systems respond rapidly to climate fluctuations. A 4.4 m thick laminated diatom ooze deposited during the last deglaciation is examined from a marine sediment core (ODP Site 1098) recovered from Basin I, Palmer Deep, western Antarctic Peninsula. This deglacial laminated interval was deposited directly over a glaciomarine diamict, hence during a globally recognised period of rapid climate change. The ultra-high-resolution deglacial record is analysed using SEM backscattered electron imagery and secondary electron imagery. Laminated to thinly bedded orange-brown diatom ooze (near monogeneric Hyalochaete Chaetoceros spp. resting spores) alternates with blue-grey terrigenous sediments (open water diatom species). These discrete laminae are interpreted as austral spring and summer signals respectively, with negligible winter deposition. Sub-seasonal sub-laminae are observed repeatedly through the summer laminae, suggesting variations in shelf waters throughout the summer. Tidal cycles, high storm intensities and/or intrusion of Circumpolar Deep Water onto the continental shelf introduced conditions which enhanced specific species productivity through the season.

Recently, Early Warning Signals (EWS) have been developed to predict tipping points in Earth Systems. This discussion highlights the potential to apply EWS to human social and economic systems, which may also undergo similar critical transitions. Social tipping points are particularly difficult to predict, however, and the current formulation of EWS, based on a physical system analogy, may be insufficient. As an alternative set of EWS for social systems, we join with other authors encouraging a focus on heterogeneity, connectivity through social networks and individual thresholds to change.