Long-term monitoring and analyses of physical factors regulating variability in coastal Antarctic phytoplankton biomass, in situ productivity and taxonomic composition over subseasonal, seasonal and interannual time scales

Abstract

A 3 yr high-resolution temporal data base related to phytoplankton dynamics was collected during the austral spring/sumrner periods of 1991 to 1994 in shelf waters adjacent to Palmer Statlon, Antarctica. Here, the data base is used [ l ) to quantlfy the vanabillty in phytoplankton biomass, In sjtu productivity and taxonomic composition over subseasonal, seasonal and interannual time scales; (2) to elucidate environmental mechanisms controlling these temporal patterns; and (3) to ascertain which phytoplankton markers are most suitable-for detecting longer-term (i.e. decadal) trends in phytoplankton dynamlcs in coastal waters of the Southel-n Ocean. The Long-Term Ecological Research (LTER) coastal study sites showed hlgh interannual var~abillty In peak phytoplankton blomass (75 to 494 mg chl a m-') and integrated pnmary productlon 11.08 to 6.58 g C m -' d ' ) . Seasonal and annual patterns in biomass and productivity were shown to be driven by shorter-t~me-scale phys~cal forcing by local wind stress. Low daily wind speeds (c10 m S") were associated with water-column stabilization. However, extended periods ( > l wk) of low wind stress were required for increased phytoplankton growth and biomass accumulation. Temperature data supports the view that water masses can be replaced on time scales of a less than a day to a few days In these coastal waters. Such disruptions are associated with abrupt changes in local pnmary productlon and may lead to sudden shifts In local phytoplankton community structure. Desp~te the high seasonal and interannual variability in b~o m a s s and associated In situ productivity in this coastal environment, the replacement sequence of one dominant phytoplankton group by another was very similar on subseasonal time scales for all 3 years. LVe suggest that changes i n phytoplankton successional patterns may be a more sensitive marker for detecting long-term trends in Southern Ocean ecosystems than either biomass or productivity indices, where short-term variability of the latter IS as great or greater than interannual variations documented to date

Southern Ocean phytoplankton physiology in a changing climate

“…Changes in the microbial community are difficult to quantify against a high background of temporal and spatial variability, but evidence indicates that dinoflagellate (Hallegraeff, 2010;McLeod et al, 2012) and Emiliania huxleyi (Cubillos et al, 2007) distributions are migrating poleward. Similarly, increased precipitation and glacial melt from warmer temperatures reportedly favours dominance of cryptophytes over diatoms in Antarctic coastal waters (Moline and Prézelin, 1996;Moline et al, 2004). In addition, the timing, duration and magnitude of phytoplankton blooms is defined by the impact of temperature on the physical environment (e.g.…”

Variability of Primary Production in an Antarctic Marine Ecosystem as Estimated Using a Multi-scale Sampling Strategy

“…Primary production in the WAP area follows closely the distribution of phytoplankton biomass measured as chlorophyll a (chl-a) concentration, and published values show a wide range of spatial and temporal variability (Smith et al, 1996a(Smith et al, , 1998aMoline and Prezelin, 1996). Concentrations are greatest nearshore with an onshore/offshore gradient of decreasing biomass towards the continental slope that follows a gradient in bottom topography and physical and optical properties (Smith et al, 1996a(Smith et al, , 1998c.…”

“…Data averaged for nearshore stations (B & E) and presented as a function of time during the growing season from 1991/92 through 1998/99. Data for the 1991/92 through 1993/94 season are estimated using photosynthesis irradiance curves integrated to 60 m (Moline and Prezelin, 1996). Data from 1994/95 through 1999/00 estimated from simulated in situ observations (SIS), as described in the text, integrated to the depth representing 2% of surface irradiance.…”

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

“…In general, phytoplankton blooms around the AP are typically associated with the development of a shallow mixed layer (retaining phytoplankton within adequate light levels) and with iron availability (e.g., Prézelin et al, 2000), and are reported to be typically dominated by diatoms and/or haptophytes (primarily P. antarctica). Nevertheless, several studies have highlighted the increasing importance of cryptophytes in the AP as they prevail over diatoms, particularly within ice melting regions (Moline and Prézelin, 1996;Moline et al, 2004). Several other studies have related the seasonal succession of phytoplankton along the west of the AP (wAP) to the timing of the sea ice retreat, particularly from the south of Gerlache Strait to Marguerite Bay (Garibotti et al, 2005;Prézelin et al, 2000), with some evidence found within the BS (Mendes et al, 2013;Varela et al, 2002).…”

“…Firstly, diatom blooms attain higher biomass when the sea ice retreat is under way and, with a continued stratification, cryptophytes can numerically replace these diatoms (Ducklow et al, 2007). Finally, a phytoplankton community co-dominated primarily by very small diatoms and other unidentified flagellates are associated with low Chl-a (Garibotti et al, 2005;Moline and Prézelin, 1996). There are numerous sources in the literature on phytoplankton dynamics in some wAP systems, principally near Marguerite Bay (Prézelin et al, 2004 and references therein).…”