Abstract

A phytoplankton bloom occurred in Ardley Cove, King George Island in January 2016, during which maximum chlorophyll-a reached 9.87 mg/m3. Records show that blooms have previously not occurred in this area prior to 2010 and the average chlorophyll-a concentration between 1991 and 2009 was less than 2 mg/m3. Given the lack of in situ measurements and the poor performance of satellite algorithms in the Southern Ocean and Antarctic waters, we validate and assess several chlorophyll-a algorithms and apply an improved baseline fluorescence approach to examine this bloom event. In situ water properties including in vivo fluorescence, water leaving radiance, and solar irradiance were collected to evaluate satellite algorithms and characterize chlorophyll-a concentration, as well as dominant phytoplankton groups. The results validated the nFLH fluorescence baseline approach, resulting in a good agreement at this high latitude, high chlorophyll-a region with correlation at 59.46%. The dominant phytoplankton group within the bloom was micro-phytoplankton, occupying 79.58% of the total phytoplankton community. Increasing sea ice coverage and sea ice concentration are likely responsible for increasing phytoplankton blooms in the recent decade. Given the profound influence of climate change on sea-ice and phytoplankton dynamics in the region, it is imperative to develop accurate methods of estimating the spatial distribution and concentrations of the increasing occurrence of bloom events.

Highlights

  • Due to the extreme climate and the difficulties of conducting field research above 60◦ south, the Southern Ocean (SO), especially around Antarctica, lacks a systematic in situ sampling program of its peculiar bio-optics and micro-organism community structure [1,2,3]

  • A phytoplankton bloom occurred in Ardley Cove near King George Island (KGI) in January

  • Low chlorophyll-a concentrations occurred in the Great Wall Cove, reaching only 1.37 mg/m3

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Summary

Introduction

Due to the extreme climate and the difficulties of conducting field research above 60◦ south, the Southern Ocean (SO), especially around Antarctica, lacks a systematic in situ sampling program of its peculiar bio-optics and micro-organism community structure [1,2,3]. Compared with the global ocean, the SO has a narrower water leaving radiance in the green band [12]. This narrow gap leads to underestimation of chlorophyll-a in blue-green band ratio algorithms such as OC3 or OC4 [13,14]. Seasonal sea ice causes contaminated pixels, which underestimate chlorophyll-a in > 1.5 mg/m3 and overestimates in < 1.5 mg/m3 waters [15,16]. These are obvious patterns in the Arctic and are probably similar in Antarctica. The SO has unique aerosols and cloud coverage [17], and lacks a proper vertical atmospheric simulation to correct for aerosol influences [18]

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