Comparing springtime ice-algal chlorophyll a and physical properties of multi-year and first-year sea ice from the Lincoln Sea.

Christine Michel,Christian Haas,Connie Lovejoy,Andrea Niemi,Hauke Flores,Ido Hatam,J Alec Casey,Benjamin A Lange,Justin F Beckers,Guillaume Meisterhans

doi:10.1371/journal.pone.0122418

Abstract

With near-complete replacement of Arctic multi-year ice (MYI) by first-year ice (FYI) predicted to occur within this century, it remains uncertain how the loss of MYI will impact the abundance and distribution of sea ice associated algae. In this study we compare the chlorophyll a (chl a) concentrations and physical properties of MYI and FYI from the Lincoln Sea during 3 spring seasons (2010-2012). Cores were analysed for texture, salinity, and chl a. We identified annual growth layers for 7 of 11 MYI cores and found no significant differences in chl a concentration between the bottom first-year-ice portions of MYI, upper old-ice portions of MYI, and FYI cores. Overall, the maximum chl a concentrations were observed at the bottom of young FYI. However, there were no significant differences in chl a concentrations between MYI and FYI. This suggests little or no change in algal biomass with a shift from MYI to FYI and that the spatial extent and regional variability of refrozen leads and younger FYI will likely be key factors governing future changes in Arctic sea ice algal biomass. Bottom-integrated chl a concentrations showed negative logistic relationships with snow depth and bulk (snow plus ice) integrated extinction coefficients; indicating a strong influence of snow cover in controlling bottom ice algal biomass. The maximum bottom MYI chl a concentration was observed in a hummock, representing the thickest ice with lowest snow depth of this study. Hence, in this and other studies MYI chl a biomass may be under-estimated due to an under-representation of thick MYI (e.g., hummocks), which typically have a relatively thin snowpack allowing for increased light transmission. Therefore, we suggest the on-going loss of MYI in the Arctic Ocean may have a larger impact on ice–associated production than generally assumed.

Highlights

Arctic first-year sea ice (FYI), from lower latitude and shelf regions, is generally more productive than multi-year ice (MYI), which leads to the assumption that a replacement of MYI by FYI will result in an overall increase of sea ice algal biomass
MYI had lower variability between site-averaged snow depth values, FYI had lower variability when considering each site individually. This was illustrated by the mean of site standard deviations for FYI snow depth: 0.08 m, compared to MYI: 0.17 m
The total thickness of the MYI cores remained within the broader thickness distribution they do not represent the thicker end of a typical ice distribution in the Lincoln Sea

Summary

Introduction

Arctic first-year sea ice (FYI), from lower latitude and shelf regions, is generally more productive than multi-year ice (MYI), which leads to the assumption that a replacement of MYI by FYI will result in an overall increase of sea ice algal biomass. The decline of summer sea ice has occurred concurrently with an increase in duration of the melt season and changes in the timing of melt onset and freeze-up [5,6,7,8]. These findings in conjunction with climate-model simulations [9,10,11,12] demonstrate that continued Arctic warming and declining Arctic sea ice, with the replacement of MYI by FYI, is likely to continue unabated into the future, having profound consequences for climate feed-backs, physical ocean processes, ecosystem linkages, and Arctic biodiversity [5,13]. Changes in ice algal biomass and distribution are expected to strongly impact Arctic food webs and the Arctic carbon cycle, which can have cascading impacts on global-scale ecological interactions and the global carbon budget

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