Impact of sea ice on the marine iron cycle and phytoplankton productivity

S. Wang,K. Lindsay,D. Bailey,M. Holland,J. K. Moore

doi:10.5194/bg-11-4713-2014

S. Wang, K. Lindsay + Show 3 more

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https://doi.org/10.5194/bg-11-4713-2014

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Abstract

Abstract. Iron is a key nutrient for phytoplankton growth in the surface ocean. At high latitudes, the iron cycle is closely related to the dynamics of sea ice. In recent decades, Arctic sea ice cover has been declining rapidly and Antarctic sea ice has exhibited large regional trends. A significant reduction of sea ice in both hemispheres is projected in future climate scenarios. In order to adequately study the effect of sea ice on the polar iron cycle, sea ice bearing iron was incorporated in the Community Earth System Model (CESM). Sea ice acts as a reservoir for iron during winter and releases the trace metal to the surface ocean in spring and summer. Simulated iron concentrations in sea ice generally agree with observations in regions where iron concentrations are relatively low. The maximum iron concentrations simulated in Arctic and Antarctic sea ice are much lower than observed, which is likely due to underestimation of iron inputs to sea ice or missing mechanisms. The largest iron source to sea ice is suspended sediments, contributing fluxes of iron of 2.2 × 108 mol Fe month−1 in the Arctic and 4.1 × 106 mol Fe month−1 in the Southern Ocean during summer. As a result of the iron flux from ice, iron concentrations increase significantly in the Arctic. Iron released from melting ice increases phytoplankton production in spring and summer and shifts phytoplankton community composition in the Southern Ocean. Results for the period of 1998 to 2007 indicate that a reduction of sea ice in the Southern Ocean will have a negative influence on phytoplankton production. Iron transport by sea ice appears to be an important process bringing iron to the central Arctic. The impact of ice to ocean iron fluxes on marine ecosystems is negligible in the current Arctic Ocean, as iron is not typically the growth-limiting nutrient. However, it may become a more important factor in the future, particularly in the central Arctic, as iron concentrations will decrease with declining sea ice cover and transport.

Highlights

Sea ice covers a large portion of the high-latitude ocean, and it is very vulnerable to climate change
This work is based on the marine ecosystem and biogeochemistry module of the Community Earth System Model (CESM), which is known as the Biogeochemical Elemental Cycling (BEC) model (Moore et al, 2002, 2004)
Iron sequestration and transport by sea ice are incorporated into the CESM-BEC model to study the role of sea ice in the marine iron cycle, with a full assessment of the impacts on biology

Summary

Introduction

Sea ice covers a large portion of the high-latitude ocean, and it is very vulnerable to climate change. Overall the Antarctic sea ice remains relatively unchanged. While there is a mild increase in ice cover (Kurtz and Markus, 2012), there are strong interannual variations in coverage (Oza et al, 2011) and large regional trends (Parkinson and Cavalieri, 2012). Climate projections suggest that sea ice will decline rapidly in future decades in both hemispheres (Holland et al, 2006; Stroeve et al, 2012). Timing of the onset of ice formation and melting will change (Boe et al, 2009)

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