Coastal zone color scanner pigment concentrations in the Southern Ocean and relationships to geophysical surface features

Abstract

The spatial and seasonal distributions of phytoplankton pigment concentration over the entire southern ocean have been studied for the first time using the coastal zone color scanner historical data set (from October 1978 through June 1986). Enhanced pigment concentrations are observed between 35øS and 55øS throughout the year, with such enhanced regions being more confined to the south in the austral summer and extending further north in the winter. North and south of the polar front, phytoplankton blooms (>1 mg/m 3) are not uniformly distributed around the circumpolar region. Instead, blooms appear to be located in regions of ice retreat (or high melt areas) such as the ScotiaSea and the Ross Sea, in relatively shallow areas (e.g., the Patagonian and the New Zealand shelves), in some regions of Ekman upwelling like the Tasman Sea, and near areas of high eddy kinetic energy such as the Agulhas retroflection. Among all features examined by regression analysis, bathymetry appears to be the one most consistently correlated with pigments (correlation coefficient being about -0.3 for the entire region). The cause of negative correlation with bathymetry is unknown but is consistent with the observed abundance of iron in shallow areas in the Antarctic region. It is also consistent with resuspension of phytoplankton cells by wind-induced mixing, especially in shallow waters. On the other hand, in the deep ocean (especially at latitudes <45øS where surface nutrients may be limiting), upwelling induced by topographic features may cause resupply of nutrients to the surface and shoaling of the subsurface chlorophyll maximum. Low pigment values are common at low latitudes and in regions of high wind stress, where deep mixing and net loss of surface pigment occur. Nutrients (phosphate, nitrate, and silicate) are found to correlate significantly with pigments when the entire southern ocean is considered, but south of 55øS the correlation is poor, probably because the Antarctic waters are not nutrient limited. Nutrients are also highly correlated with Ekman upwelling. Although cloud cover and normalized aerosol radiance are correlated to the patterns of pigment concentrations in some areas, the correlations are weak in other areas, suggesting that light and iron may not be the primary factors responsible for the spatial variability of pigment concentrations, especially during summer. Large interannual variability (>30%) in average pigment concentration over the entire region during different seasons indicates possible influence of time dependent parameters. 1.

The US Southern Ocean Joint Global Ocean Flux Study: an introduction to AESOPS

“…The seasonal changes in ice cover on the Ross Sea continental shelf were similar to those found in previous years ( Fig. 2a; Comiso et al, 1993). The polynya formed close to the ice shelf in late winter, likely due to katabatic winds blowing o!…”

Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

“…3 . This gradient is most pronounced for silicate, most no-Ž tably in the east Pacific region of our study Plate 3 of Comiso et al, 1993;Sullivan et al, 1993, their . Fig.…”

Influence of oceanographic features on spatial and interannual variability of phytoplankton in the Bransfield Strait, Antarctica

“…The Southern Ocean is widely recognized as a high nutrient, low Chl-a zone (HNLC) (Hoppema et al, 2003) in which phytoplankton development is considered to be iron-limited (Boyd et al, 2000;Feng et al, 2010;Martin et al, 1990a,b). As demonstrated in previous studies, variations in both Chl-a and primary production within the Southern Ocean could be associated with environmental factors such as fronts and upwelling (Bathmann et al 1997;Jacques and Panouse, 1991;Lovenduski and Gruber, 2005), as well as the proximity to the coast or islands (Blain et al 2001;Comiso et al 1993;Hoppema et al, 2003), where iron availability is be periodically enhanced. In addition, it has been established that a sunlit, shallow mixed layer depth (Mitchell and Holm-Hansen, 1991;Nelson and Smith, 1991) combined with an iron supply would count as two major factors or co-factors affecting phytoplankton dynamics in the Southern Ocean (Arrigo et al, 1999).…”