Freshwater control of onset and species composition of Greenland shelf spring bloom

Abstract

. The phytoplankton community in the melting ice zone consisted of Phaeocystis sp., small flagellates (< 4 µm) and picoplankton, while diatoms were less abundant. Phaeocystis sp. contributed up to 15 g C m -2 to the carbon biomass (70% of total carbon measured), whereas the contribution of diatoms and flagellates to carbon biomass was relatively low, with up to 1.2 g C m -2 (5.7%) and up to 2.5 g C m -2 (11.7%), respectively. On the shelf the bloom starts at the very beginning of stabilisation (elevated N 2 values) which results solely from the release of meltwater. The locally restricted water stability leads to a patchy phytoplankton distribution in the Irminger Sea.

Timing of nutrient depletion, diatom dominance and a lower-boundary estimate of export production for Irminger Basin, North Atlantic

“…Export production was estimated as that portion of the daily total production which occurred between the start of the bloom and the day when silica first droped below 2 µmol l . This is comparable to in situ estimates based on nitrate drawdown, which ranged from 35 to 60 g C m -2 yr -1 (Henson et al 2003, Sanders et al 2005, Waniek et al 2005.…”

“…bloom on the NE Greenland shelf (Waniek et al 2005). During most of the cruise in late April and early May, diatoms were not observed at bloom concentrations, with the exception of the Reykjanes Ridge at the end of the cruise in mid-May, where the abundance of diatoms had increased substantially (see cruise track in Fig.…”

“…This is a region where the cold, fresh, meltwater run-off promotes stratification early in spring and the growth of dense blooms of Phaeocystis sp. (Waniek et al 2005). The unusual hydrographic properties of the coastal region suggest that a separate relationship is required.…”

“…Satellite-based estimates suggest an annual mean export of ~100 to 150 g C m -2 (Falkowski et al 1998, Laws et al 2000, which is in contrast to new production estimates based on in situ measurements of nitrate drawdown, which range from ~35 to 60 g C m -2 (Henson et al 2003, Sanders et al 2005, Waniek et al 2005. Currently, global estimates of primary and export production can only be made with sufficient spatial and temporal resolution using satellite databased methods.…”

Physical controls and mesoscale variability in the Labrador Sea spring phytoplankton bloom observed by Seaglider

“…Thin layers can be formed by several mechanisms, including the shearing of an initially thick layer of plankton or nutrients (Ryan et al, 2008;Birch et al, 2008;Stacey et al, 2007), aggregation at a particular isopycnal (Dekshenieks et al, 2001;Alldredge et al, 2002), or surface depletion of nutrients resulting in plankton aggregating at the intersection of the pycnocline and nutricline. Thin layers were observed on the eastern shelf of Greenland (Waniek et al, 2005). In this case, nutrients were not limiting in the surface layer, and the authors suggested that the thin layer results from a sinking layer of biomass or pressure from grazing zooplankton.…”