From the chlorophyll <i>a</i> in the surface layer to its vertical profile: a Greenland Sea relationship for satellite applications

Abstract

Abstract. Current estimates of global marine primary production range over a factor of two. Improving these estimates requires an accurate knowledge of the chlorophyll vertical profiles, since they are the basis for most primary production models. At high latitudes, the uncertainty in primary production estimates is larger than globally, because here phytoplankton absorption shows specific characteristics due to the low-light adaptation, and in situ data and ocean colour observations are scarce. To date, studies describing the typical chlorophyll profile based on the chlorophyll in the surface layer have not included the Arctic region, or, if it was included, the dependence of the profile shape on surface concentration was neglected. The goal of our study was to derive and describe the typical Greenland Sea chlorophyll profiles, categorized according to the chlorophyll concentration in the surface layer and further monthly resolved profiles. The Greenland Sea was chosen because it is known to be one of the most productive regions of the Arctic and is among the regions in the Arctic where most chlorophyll field data are available. Our database contained 1199 chlorophyll profiles from R/Vs Polarstern and Maria S. Merian cruises combined with data from the ARCSS-PP database (Arctic primary production in situ database) for the years 1957-2010. The profiles were categorized according to their mean concentration in the surface layer, and then monthly median profiles within each category were calculated. The category with the surface layer chlorophyll (CHL) exceeding 0.7 mg C m −3 showed values gradually decreasing from April to August. A similar seasonal pattern was observed when monthly profiles were averaged over all the surface CHL concentrations. The maxima of all chlorophyll profiles moved from the greater depths to the surface from spring to late summer respectively.The profiles with the smallest surface values always showed a subsurface chlorophyll maximum with its median magnitude reaching up to three times the surface concentration. While the variability of the Greenland Sea season in April, May and June followed the global non-monthly resolved relationship of the chlorophyll profile to surface chlorophyll concentrations described by the model of Morel and Berthon (1989), it deviated significantly from the model in the other months (July-September), when the maxima of the chlorophyll are at quite different depths. The Greenland Sea dimensionless monthly median profiles intersected roughly at one common depth within each category. By applying a Gaussian fit with 0.1 mg C m −3 surface chlorophyll steps to the median monthly resolved chlorophyll profiles of the defined categories, mathematical approximations were determined. They generally reproduce the magnitude and position of the CHL maximum, resulting in an average 4 % underestimation in C tot (and 2 % in rough primary production estimates) when compared to in situ estimates. These mathematical approximations can be used as the input to the satellite-based p...

Bio‐optical Properties of Surface Waters in the Atlantic Water Inflow Region off Spitsbergen (Arctic Ocean)

“…On average Chl a was lowest in 2013 (0.87 mg/m 3 ), highest in 2014 (1.58 mg/m), and slightly lower in 2015 (1.39 mg/m; Makarewicz et al, ). This is in a similar range as reported by Stramska et al (, ), Cherkasheva et al (, ), and Liu et al () in the same region. The particulate absorption coefficient was tightly coupled with phytoplankton biomass (Figure ); therefore, year‐to‐year changes in a p (443) largely reflected the year‐to‐year changes in Chl a .…”

“…Additional instrumental observations and sampling for Chl a and particulate absorption were conducted onboard R/V Lance (Norwegian Polar Institute) in late August 2014 (Fram Strait expedition, FS2014) on a transect across the eastern Fram Strait along 78.9°N, parallel to section EB2 (Figure ) to examine seasonal variability of IOPs and bio‐optics. According to a previous studies in this region by Cherkasheva et al (, ), typically phytoplankton blooms (Chl a > 1 mg/m 3 ) begin in May, peak in June, and last through July. Based on those findings, we assumed that most of measurements of optical and bio‐optical parameters took place in the period when the phytoplankton communities were in a stationary phase.…”

Assessing Phytoplankton Activities in the Seasonal Ice Zone of the Greenland Sea Over an Annual Cycle

“…During the ice edge phase, satellite observations of [Chl a] (only available in 2012) were in the range of previously published data of ice edge bloom observations in the Greenland Sea (maximum around 1 mg/m 3 , Perrette et al, 2011) but rapidly decreased, even though an increase of the [Chl a] at the SCM was ongoing (Figure 7). BGC-Argo float observations of [Chl a] averaged within the first optical depth (0-10 m in the Greenland Sea, Cherkasheva et al, 2013) also decreased during this phase (Figure 7). This suggests that satellite [Chl a] estimations at the ice edge may miss substantial phytoplankton biomass accumulation at depth (e.g., Hill et al, 2013).…”

Photophysiological state of natural phytoplankton communities in the South China Sea and Sulu Sea

“…2) were calculated which ranged from −18.13 % to 15.75 %, with an average value of −10.98 % and a minimum value of −6.20 %. Compared to other studies (e.g., Lee et al, 2007;Milutinović, 2011;Cherkasheva et al, 2013) during the underway transect. The FRR fluorometers were programmed to deliver flash sequence consisting of a series of 100 subsaturation flashlets at 1.1 µs duration and 2.8 µs intervals followed by a series of 20 relaxation flashlets (1.1 µs flash duration and 51.6 µs intervals.…”