ALBERT

Description: Redox-sensitive trace metals (Mn, Fe, U, Mo, Re), nutrients and terminal metabolic products (NO3-, NH4+, PO43-, total alkalinity) were investigated for the first time in pore waters of Antarctic coastal sediments. The results of this study reveal a high spatial variability in redox conditions in surface sediments from Potter Cove, King George Island, western Antarctic Peninsula. Particularly in the shallower areas of the bay the significant correlation between sulphate depletion and total alkalinity, the inorganic product of terminal metabolism, indicates sulphate reduction to be the major pathway of organic matter mineralisation. In contrast, dissimilatory metal oxide reduction seems to be prevailing in the newly ice-free areas and the deeper troughs, where concentrations of dissolved iron of up to 700 μM were found. We suggest a combination of several factors to be responsible for the domination of metal oxide reduction over sulphate reduction in these areas. These include the increased accumulation of fine-grained material with high amounts of reducible metal oxides, a reduced availability of metabolisable organic matter and an enhanced physical and biological disturbance by bottom water currents, ice scouring and burrowing organisms. Based on modelled iron fluxes we calculate the contribution of the Antarctic shelf to the pool of potentially bioavailable iron (Feb) to be 6.9 × 103 to 790 × 103 t yr-1. Consequently, these shelf sediments would provide an Feb flux of 0.35-39.5 mg m-2 yr-1 (median: 3.8 mg m-2 yr-1) to the Southern Ocean. This contribution is in the same order of magnitude as the flux provided by icebergs and significantly higher than the input by aeolian dust. For this reason suboxic shelf sediments form a key source of iron for the high nutrient-low chlorophyll (HNLC) areas of the Southern Ocean. This source may become even more important in the future due to rising temperatures at the WAP accompanied by enhanced glacier retreat and the accumulation of melt water derived iron-rich material on the shelf.

Description: Key Points: • Antarctic meltwater forcing induces an overall global cooling but regional warming in East Asia • Antarctic meltwater forcing can shift the Intertropical Convergence Zone northward and suppress convection over the Western North Pacific • Suppressed convection in the Western North Pacific is responsible for the regional warming of East Asia via atmospheric teleconnection. In recent decades, Antarctic ice sheet/shelf melting has been accelerated, releasing freshwater into the Southern Ocean. It has been suggested that the meltwater flux could lead to cooling in the Southern Hemisphere, which would retard global warming and further induce a northward shift of the Intertropical Convergence Zone (ITCZ). In this study, we use experimental ensemble climate simulations to show that Antarctic meltwater forcing has distinct regional climate impacts over the globe, leading in particular to regional warming in East Asia, which offsets the global cooling effect by the meltwater forcing. It is suggested that Antarctic meltwater forcing leads to a negative precipitation anomaly in the Western North Pacific (WNP) via cooling in the tropics and the northward shift of the ITCZ. This suppressed convection in WNP induces an anticyclonic flow over the North Pacific, which leads to regional warming in East Asia. This hypothesis is supported by analyses of interensemble spread and long-term control simulations.

Description: Sedimentary evidence for enhanced volcanic eruption during the glacial/interglacial transition in the volcanically active mid-ocean ridges is still lacking. Here, we present the sedimentary records of enhanced deglacial volcanic activity in a well-dated sediment core from the middle part of Central Indian Ridge (CIR), which can provide clue for comprehensively understanding of the temporal relation of increase in submarine volcanism relative to glacial/interglacial transition. Notably, the 35-kyr sediment core used in this study contains continuous, discernible pyroclastic deposit layers (0.5–5 cm thick), which are composed mainly of angular and curved fluidal shards with vesicles, possibly suggesting volatile-rich ridge eruptions. High-resolution elemental profiles of the core provide definite records of at least 17 volcanic eruptions during the past 35 kyr. Interestingly, volcanism was sparse during the Last Glacial Maximum (LGM), but increased significantly during the last deglaciation after ~18 kyr BP. The last deglaciation-associated volcanic eruptions in the CIR may be linked to decompression melting during the LGM sea-level lowstand, reaffirming an influence of sea level variability on global ocean ridge magmatism. Combining the previous results, furthermore, simultaneous strengthening of submarine and subaerial volcanic eruptions during the last deglaciation could have accelerated the rise of atmospheric CO2, with the ensuing warming constituting positive feedback upon deglaciation. Highlights • A succession of pyroclastic records in a well-dated sediment core from the CIR was identified. • The morphologies of the pyroclasts are consistent with volatile-rich submarine eruption. • Deglaciation-associated enhanced volcanism seems robust in the mid-ocean ridges. • Tentative support for a link between ridge volcanism and climate change is provided.