Analysis of Physical and Biogeochemical Control Mechanisms on Summertime Surface Carbonate System Variability in the Western Ross Sea (Antarctica) Using In Situ and Satellite Data

Paola Rivaro,Pierpaolo Falco,Silvia Sandrini,Clara Manno,Pasquale Castagno,Carmela Ianni,Lorenza Raimondi,Yuri Cotroneo

doi:10.3390/rs11030238

Abstract

In this study, carbonate system properties were measured in the western Ross Sea (Antarctica) over the 2005–2006 and 2011–2012 austral summers with the aim of analysing their sensitivity to physical and biogeochemical drivers. Daily Advanced Microwave Scanning Radiometer 2 (AMSR2) sea ice concentration maps, obtained prior to and during the samplings, were used to analyse the sea ice evolution throughout the experiment periods. Monthly means and 8-day composite chlorophyll concentration maps from the Moderate-resolution Imaging Spectroradiometer (MODIS) Aqua satellite at 4-km resolution were used to investigate inter-annual and basin scale biological variability. Chlorophyll-a concentrations in surface waters estimated by MODIS satellite data contribute to descriptions of the variability of carbonate system properties in surface waters. Mean values of carbonate system properties were comparable across both investigated years; however, the 2012 data displayed larger variability. Sea ice melting also had a pivotal role in controlling the carbonate system chemistry of the mixed layer both directly through dilution processes and indirectly by favouring the development of phytoplankton blooms. This resulted in high pH and ΩAr, and in low CT, particularly in those areas where high chlorophyll concentration was shown by satellite maps.

Highlights

The Southern Ocean (SO) is highly sensitive to anthropogenic atmospheric carbon dioxide (CO2) increases, as the cold waters are naturally CO2-rich and have a low total alkalinity (AT) to total inorganic carbon (CT) ratio, which reduces the degree of carbonate mineral saturation and the buffering capacity for further CO2 uptake [1,2]
Our results show the seasonal influence of both sea ice melting and biological production in driving summertime Antarctic surface water (AASW) carbonate system variability in the western Ross Sea
This study highlights the pivotal role of sea ice melting in controlling both directly and indirectly the carbonate

Summary

Introduction

The Southern Ocean (SO) is highly sensitive to anthropogenic atmospheric carbon dioxide (CO2) increases, as the cold waters are naturally CO2-rich and have a low total alkalinity (AT) to total inorganic carbon (CT) ratio, which reduces the degree of carbonate mineral saturation and the buffering capacity for further CO2 uptake [1,2]. CO2 addition lowers the saturation state (Ω) of calcium carbonate in a process called ocean acidification (OA) [3,4]. Surface waters of the SO are predicted to experience wintertime carbonate under-saturation, which is driven by seasonal variations in biological activities and a combination of reduced sea-ice cover, surface water freshening, and increased air-sea CO2 exchange, by 2030 [5,6]. These changes in carbonate chemistry could have severe consequences for calcifying organisms. Live shell dissolution of shelled pteropods in the SO has been already reported [5,7,8]

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Results

Discussion

Conclusion