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J., LIMNOLOGY O IN PRESS Wallace MI, 2008, DEEP-SEA RES PT II, V55, P2023, DOI 10.1016/j.dsr2.2008.04.033 Annett, Amber L. Henley, Sian F. Van Beek, Pieter Souhaut, Marc Ganeshram, Raja Venables, Hugh J. Meredith, Michael P. Geibert, Walter Antarctic Science Bursary; National Environment Research Council, UK; British Council-EGIDE ALLIANCE/Franco-British Research Partnership Programme; NSERC; University of Edinburgh The authors would like to thank the Rothera Research Station marine staff, in particular Danny Edmunds, for help with sample collection, and the British Antarctic Survey for logistical support. Jan Scholten at the International Atomic Energy Agency in Monaco kindly provided standards, and helpful discussion regarding methodology. The editor (L. Padman) and two anonymous reviewers provided valuable comments to improve the manuscript. This work was supported by an Antarctic Science Bursary, Collaborative Gearing Scheme funding (through the National Environment Research Council, UK), the British Council-EGIDE ALLIANCE/Franco-British Research Partnership Programme, an NSERC scholarship and the University of Edinburgh. 3 CAMBRIDGE UNIV PRESS NEW YORK ANTARCT SCI ; In the western Antarctic Peninsula region, micronutrient injection facilitates strong plankton blooms that support productive food webs, unlike large areas of the low-productivity Southern Ocean. We use naturally occurring radioisotopes of radium to constrain rates of chemical fluxes into Ryder Bay (a small coastal embayment in northern Marguerite Bay), and hence to evaluate possible sources of sediment-derived micronutrients and estimate sediment-ocean mixing rates. We present the first coupled, short-lived radium isotope (Ra-223 and Ra-224) measurements from Antarctic waters, both present at very low activities (mean 0.155 and 3.21 dpm m(-3), respectively), indicating much lower radium inputs than in other coastal environments. Longer-lived Ra-228 activity was also lower than existing nearshore values, but higher than open ocean waters, indicating some degree of coastal radium input on timescales exceeding the week-to-month range reflected by Ra-223 and Ra-224. Using a simple diffusion model along a shore to mid-bay transect, effective horizontal eddy diffusivity estimates ranged from 0.22-0.83m(2) s(-1) from Ra-223 and Ra-224, respectively, much lower than already-low mixing estimates for the Southern Ocean. Significant radium enrichment and much faster mixing (18m(2) s(-1)) was found near a marine-terminating glacier and consequently any sediment-derived micronutrient inputs in this location are more probably dominated by glacial processes than groundwater, land runoff, or marine sediment sources.