Ocean colour estimates of particulate organic carbon reservoirs in the global ocean – revisitedby Malgorzata Stramska, Agata Cieszyńska

International Journal of Remote Sensing

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Year
2015
DOI
10.1080/01431161.2015.1049380
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Earth and Planetary Sciences (all)

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Ocean colour estimates of particulate organic carbon reservoirs in the global ocean – revisited

Malgorzata Stramskaab & Agata Cieszyńskaab a Institute of Oceanology of the Polish Academy of Sciences, Sopot 81-712, Poland b Department of Earth Sciences, Szczecin University, Szczecin 70-383, Poland

Published online: 20 Jul 2015.

To cite this article: Malgorzata Stramska & Agata Cieszyńska (2015) Ocean colour estimates of particulate organic carbon reservoirs in the global ocean – revisited, International Journal of

Remote Sensing, 36:14, 3675-3700, DOI: 10.1080/01431161.2015.1049380

To link to this article: http://dx.doi.org/10.1080/01431161.2015.1049380

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D ow nl oa de d by [U niv ers ity of

E xe ter ] a t 0 1:0 8 3 0 J uly 20 15

Ocean colour estimates of particulate organic carbon reservoirs in the global ocean – revisited

Malgorzata Stramskaa,b* and Agata Cieszyńskaa,b aInstitute of Oceanology of the Polish Academy of Sciences, Sopot 81-712, Poland; bDepartment of Earth Sciences, Szczecin University, Szczecin 70-383, Poland (Received 19 November 2014; accepted 31 March 2015)

We have examined 16 years (1998–2013) of particulate organic carbon (POC) concentrations derived from remotely sensed ocean colour. POC concentrations vary spatially from more than 300 mg m−3 in the northern North Atlantic in summer to about 20 mg m−3 in the oligotrophic South Pacific (16-year global average = 67.7 mg m−3). The seasonal variability is weak at lower latitudes and stronger at higher latitudes. The annual mean surface POC concentrations show statistically significant regional trends (p < 0.05, 95% confidence level), and are decreasing in the North Atlantic and North Pacific and increasing in the South Pacific and

Southern Oceans. The global trend is not significant. The 16-year global average water column POC biomass integrated over the euphotic depth, the mixed layer depth, or based on a combination of these two depths is estimated to be about 3.97, 3.92, and 5.03 g m−2, respectively. Water column integrated biomass shows different spatial and seasonal patterns than the surface POC concentrations, and is increasing in many ocean regions. Globally averaged POC biomass is also increasing. At the same time ocean colour data indicate a decrease in the global oceanic productivity (PP). This means that there is a negative trend in the ratio of PP to POC biomass almost everywhere in the ocean. Such a decrease could indicate that the biological pump in the ocean is weakening, but longer time series of the ocean colour data are needed to confirm this observation. 1. Introduction

The ocean plays an important role in the Earth’s carbon cycle. The total amount of carbon stored in the ocean is about 50 times greater than in the atmosphere. It has been estimated that about 50% of the carbon emitted to the atmosphere by fossil fuel burning is sequestered into the oceans (IPCC 2007). The living phytoplankton component of particulate organic carbon (POC) contributes about 50% of the global primary production on the Earth (Behrenfeld et al. 2005).

Biologically driven sequestration of carbon from the atmosphere to the deep sea, called the biological pump, consists of the soft-tissue pump and the carbonate pump where hard tissues are created (e.g. Longhurst and Harrison 1989). The biological pump operates in three phases. In the first phase, the carbon is fixed into soft or hard tissues by planktonic phototrophs in the euphotic layer of the ocean. Once this carbon is fixed, the organisms either stay in the euphotic zone and are recycled as part of the regenerative nutrient cycle, or continue to the second phase of the biological pump if they sink to the ocean floor. The sinking particles often form aggregates, increasing their sinking velocity *Corresponding author. Email: mstramska@wp.pl, mstramska@yahoo.com

International Journal of Remote Sensing, 2015

Vol. 36, No. 14, 3675–3700, http://dx.doi.org/10.1080/01431161.2015.1049380 © 2015 Taylor & Francis

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E xe ter ] a t 0 1:0 8 3 0 J uly 20 15 (e.g. Honjo et al. 2008; Siegel et al. 2014). Organic carbon in these particles is partly decomposed by bacteria during the sinking process or after the particles settle on the sea floor. In the third phase of the biological pump, carbon can be remineralized and used again in primary production. Particles that avoid remineralization are buried in the sediments and may remain there for thousands of years. It is the carbon stored in these particles that is responsible for ultimately lowering the atmospheric CO2 concentration (e.g. Siegel et al. 2014).