Seasonal and Interannual Variability of Calcite in the SubPolar North Atlantic (original) (raw)
Related papers
Geophysical Research Letters, 2006
1] The timing and duration of coccolithophore blooms along the Patagonian shelf break, as well as insights on the mechanisms that drive and maintain these blooms, were analyzed using time series of chlorophyll chl a, calcite, and sea-surface temperature (SST) derived from remote sensing data (SeaWiFS and AVHRR) and historic hydrographic data. The seasonal variability and succession of phytoplankton groups respond to light intensity and nutrient supply within the mixed layer due to seasonal changes in stratification. The early spring bloom is diatomdominated and starts in September under nutrient-rich Malvinas waters when the mixed layer begins to shallow (<80 m), and peaks around November with mixed layer depths (MLD) less than 40 m. After nutrient depletion from the spring bloom, a coccolithophore bloom begins in November when the MLD is less than 40 m, and peaks in January when the MLD reaches its minimum (18 m) and PAR reaches its maximum intensity. Citation: Signorini,
Global Biogeochemical Cycles, 2013
Coccolithophore blooms are significant contributors to the global production and export of calcium carbonate (calcite). The Patagonian Shelf is a site of intense annual coccolithophore blooms during austral summer. During December 2008, we made intensive measurements of the ecology, biogeochemistry, and physiology of a coccolithophore bloom. High numbers of Emiliania huxleyi cells and detached coccoliths (>1 × 10 3 mL À1 and >10 × 10 3 mL À1 , respectively), high particulate inorganic carbon concentrations (>10 mmol C m À2), and high calcite production (up to 7.3 mmol C m À2 d À1) all characterized bloom waters. The bloom was dominated by the low-calcite-containing B/C morphotype of Emiliania huxleyi, although a small (<10 μm) Southern Ocean diatom of the genus Fragilariopsis was present in almost equal numbers (0.2-2 × 10 3 mL À1). Estimates of Fragilariopsis contributions to chlorophyll, phytoplankton carbon, and primary production were >30%, similar to estimates for E. huxleyi and indicative of a significant role for this diatom in bloom biogeochemistry. Cell-normalized calcification rates, when corrected for a high number of nonactive cells, were relatively high and when normalized to estimates of coccolith calcite indicate excessive coccolith production in the declining phase of the bloom. We find that low measures of calcite and calcite production relative to other blooms in the global ocean indicate that the dominance of the B/C morphotype may lead to overall lower calcite production. Globally, this suggests that morphotype composition influences regional bloom inventories of carbonate production and export and that climate-induced changes in morphotype biogeography could affect the carbon cycle.
Environmental factors controlling the phytoplankton blooms at the Patagonia shelf-break in spring
Deep-sea Research Part I-oceanographic Research Papers, 2008
The shelf-break front formed between Argentinean shelf waters and the Malvinas Current (MC) flow shows a conspicuous band of high phytoplankton biomass throughout spring and summer, detected by ocean color sensors. That area is the feeding and spawning ground of several commercial species of fish and squid and is thought to play an important role in CO 2 sequestration by the ocean. Phytoplankton blooms in this area have been attributed mainly to coccolithophorids, a group of calcite-producing phytoplankton. Here we present the environmental factors associated with the spring bloom at the Patagonian shelf-break (401-481S) in the austral spring 2004. A remarkable bloom of diatoms and dinoflagellates (approximately 1200 km long) was observed along the front, where integrated chlorophyll values ranged from 90.3 to 1074 mg m À2 . It is suggested that supply of macro-nutrients by upwelling and probably iron by both upwelling and shelf transport contribute to maintaining the spring bloom. Strong water column stability along the front allowed the accumulation of algal cells mainly in the top 50 m and their maintenance in the euphotic layer. East of the shelf-break front, macronutrient levels were high (surface nitrate ¼ 16.6 mM, phosphate ¼ 0.35 mM, silicate ¼ 4.0 mM), associated with low phytoplankton biomass (o2 mg m À3 ). This was due to mixing and advection associated with the MC flow and to grazing pressure at a transitional site between the MC and the high chlorophyll patch. Primary production rates (determined by the 14 C technique) ranged between 1.9 and 7.8 g C m À2 d À1 . Primary production was highest near 421S partly because of the elevated phytoplankton biomass, which consumed most of the nitrate and phosphate in surface waters in this region. These high primary production rates are comparable with maximal seasonal productivity at eastern boundary currents. The large bloom extent at the Patagonian shelf-break (approximately 55,000 km 2 patch of 42 mg m À3 chlorophyll), the associated primary production rates and diatom dominance indicate a potentially significant biological control of gases such as O 2 and CO 2 in surface layers. The main
Journal of Plankton Research, 2009
The Spring Phytoplankton Bloom takes place in the Central Cantabrian Sea (Southern Bay of Biscay) from late-winter to spring as a series of blooms with variable biomass accumulation. In late-winter of 2004 and 2005, phytoplankton blooms occurred in this area following a change in the weather. In order to describe the dynamics of these late-winter blooms, two oceanographic cruises which involved high-frequency sampling (every 2 -3 days) were carried out. Meteorological conditions during the cruises showed similar changes in variables relevant to phytoplankton physiology and population dynamics. Before the bloom, phytoplankton started to grow actively when underwater photosynthetic active radiation (PAR) increased. However, biomass accumulation did not occur until wind, and hence turbulence levels in the water column, decreased. The observations presented here suggest that before the onset of a late-winter bloom a preliminary physiological activation phase is necessary driven by increased availability of underwater PAR. Afterwards, biomass accumulation can take place provided wind-derived water column turbulence decays. The development of the bloom is reinforced by the shoaling of the surface mixing layer depth. The timing of this sequence of events can be altered by meteorological disturbances, such as an increase of wind speed. The composition of the bloom differed across-shelf: phytoplankton larger than 5 mm in equivalent spherical diameter (ESD) dominated on the coast and inner shelf, whereas smaller phytoplankton (,5 mm ESD) were more important in the oceanic area, markedly when a frontal structure separating both domains developed at the mid-shelf.
Seasonal change of phytoplankton (spring vs. summer) in the southern Patagonian shelf
Continental Shelf Research
As part of the Patagonian Experiment (PATEX) project two sequential seasons (spring/summer 2007-2008) were sampled in the southern Patagonian shelf, when physical-chemical-biological (phytoplankton) data were collected. Phytoplankton biomass and community composition were assessed through both microscopic and high-performance liquid chromatography/chemical taxonomy (HPLC/ CHEMTAX) techniques and related to both in situ and satellite data at spatial and seasonal scales. Phytoplankton seasonal variation was clearly modulated by water column thermohaline structure and nutrient dynamics [mainly dissolved inorganic nitrogen (DIN) and silicate]. The spring phytoplankton community showed elevated biomass and was dominated by diatoms [mainly Corethron pennatum and small (o20 mm) cells of Thalassiosira spp.], associated with a deeper and more weakly stratified upper mixed layer depth (UMLD) and relatively low nutrient concentrations, which were probably a result of consumption by the diatom bloom. In contrast, the phytoplankton community in summer presented lower biomass and was mainly dominated by haptophytes (primarily Emiliania huxleyi and Phaeocystis antarctica) and dinoflagellates, associated with shallower and well-stratified upper mixed layers with higher nutrient concentrations, likely due to lateral advection of nutrient-rich waters from the Malvinas Current. The gradual establishment of a strongly stratified and shallow UMLD as season progressed, was an important factor leading to the replacement of the spring diatom community by a dominance of calcifying organisms, as shown in remote sensing imagery and confirmed by microscopic examination. Furthermore, in spring, phaeopigments a (degradation products of chlorophyll a) relative to chlorophyll a, were twice that of summer, indicating the diatom bloom was under higher grazing pressure.
2013
1] Satellite measurements allow global assessments of phytoplankton concentrations and, from observed temporal changes in biomass, direct access to net biomass accumulation rates (r). For the subarctic Atlantic basin, analysis of annual cycles in r reveals that initiation of the annual blooming phase does not occur in spring after stratification surpasses a critical threshold but rather occurs in early winter when growth conditions for phytoplankton are deteriorating. This finding has been confirmed with in situ profiling float data. The objective of the current study was to test whether satellite-based annual cycles in r are reproduced by the Biogeochemical Element Cycling-Community Climate System Model and, if so, to use the additional ecosystem properties resolved by the model to better understand factors controlling phytoplankton blooms. We find that the model gives a similar early onset time for the blooming phase, that this initiation is largely due to the physical disruption of phytoplankton-grazer interactions during mixed layer deepening, and that parallel increases in phytoplankton-specific division and loss rates during spring maintain the subtle disruption in food web equilibrium that ultimately yields the spring bloom climax. The link between winter mixing and bloom dynamics is illustrated by contrasting annual plankton cycles between regions with deeper and shallower mixing. We show that maximum water column inventories of phytoplankton vary in proportion to maximum winter mixing depth, implying that future reductions in winter mixing may dampen plankton cycles in the subarctic Atlantic. We propose that ecosystem disturbance-recovery sequences are a unifying property of global ocean plankton blooms.
Decadal variability in North Atlantic phytoplankton blooms
Journal of Geophysical Research, 2009
1] The interannual to decadal variability in the timing and magnitude of the North Atlantic phytoplankton bloom is examined using a combination of satellite data and output from an ocean biogeochemistry general circulation model. The timing of the bloom as estimated from satellite chlorophyll data is used as a novel metric for validating the model's skill. Maps of bloom timing reveal that the subtropical bloom begins in winter and progresses northward starting in May in subpolar regions. A transition zone, which experiences substantial interannual variability in bloom timing, separates the two regions. Time series of the modeled decadal variability in bloom timing show no long-term trend toward earlier or delayed blooms in any of the three regions considered here. However, the timing of the subpolar bloom does show distinct decadal-scale periodicity, which is found to be correlated with the North Atlantic Oscillation (NAO) index. The mechanism underpinning the relationship is identified as anomalous wind-driven mixing conditions associated with the NAO. In positive NAO phases, stronger westerly winds result in deeper mixed layers, delaying the start of the subpolar spring bloom by 2-3 weeks. The subpolar region also expands during positive phases, pushing the transition zone further south in the central North Atlantic. The magnitude of the bloom is found to be only weakly dependent on bloom timing, but is more strongly correlated with mixed layer depth. The extensive interannual variability in the timing of the bloom, particularly in the transition region, is expected to strongly impact the availability of food to higher trophic levels.
Spring coccolithophore production and dispersion in the temperate eastern North Atlantic Ocean
Journal of Geophysical Research, 2011
Production and dispersion of coccolithophores are assessed within their ecologic and hydrographic context across enhanced spring chlorophyll production in the surface eastern North Atlantic. Within a 4 day period from 12 to 16 March 2004, a N-S transect from 47°N to 33°N was sampled along 20°W. Water samples from defined depths down to 200 m were analyzed for coccolithophores from 0.45 mm polycarbonate filters by scanning electron microscopy. At 47°N coccolithophores flourished when euphotic conditions allowed new production at deep mixing, low temperatures, and high nutrient concentrations. Emiliania huxleyi flourished at high turbulence during an early stage of the phytoplankton succession and contributed half of the total coccolithophore assemblage, with up to 150 × 10 3 cells L −1 and up to 12 × 10 9 cells m −2 when integrated over the upper 200 m of the water column. Maximum chlorophyll concentrations occurred just north of the Azores Front, at 37°N-39°N, at comparatively low numbers of coccolithophores. To the south, at 35°N-33°N, coccolithophores were abundant within calm and stratified Subtropical Mode Waters, and E. huxleyi was the dominant species again. Although the cell densities of coccolithophores observed here remained below those typical of plankton blooms visible from satellite images, the depth-integrated total mass makes them significant producers of calcite and contributors to the total carbon sedimentation at a much wider range of ecological conditions during late winter and early spring than hitherto assumed.