Statistics for Spatial Data.

(1992). Time Series—A Biostatistical Introduction. Technometrics: Vol. 34, No. 2, pp. 229-230.

Time Series—A Biostatistical Introduction

Satellite ocean color data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) were used to examine distributions of chlorophyll concentration within the Southern Ocean for the period October 1997 through September 1998. Over most of the Southern Ocean, mean chlorophyll concentrations remained quite low ( 30°S) was estimated to be 14.2 Gt C yr−1, with most production (∼80%) taking place at midlatitudes from 30° to 50°S. Primary production at latitudes >50°S was estimated to be 2.9 Gt C yr−1. This is considerably higher than previous estimates based on in situ data but less than some recent estimates based on CZCS data. Our estimated primary production is sufficient to account for the observed Southern Hemisphere seasonal cycle in atmospheric O2 concentrations.

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Phytoplankton chlorophyll distributions and primary production in the Southern Ocean

[1] Estimates of primary production in the Southern Ocean are difficult to obtain but are essential if we are to understand its role in the global carbon cycle. Here we present a 9-year time series of daily primary production calculated from remotely sensed ocean color, sea surface temperature, and sea ice concentration using a primary production algorithm parameterized specifically for use in Southern Ocean waters. Results suggest that total annual production in waters south of 50°S averaged 1949 ± 70.1 Tg C a−1 (where a is years) between 1998 and 2006, approximately half that of previous estimates. The large but relatively unproductive pelagic province accounted for ∼90% of Southern Ocean production, while area normalized rates of production were greatest on the much smaller continental shelf (109 g C m−2 a−1). Surprisingly, production in the marginal ice zone was only slightly higher than in the pelagic province. The Ross Sea was the most productive sector of the Southern Ocean (mean = 503 Tg C a−1), followed closely by the Weddell Sea (mean = 477 Tg C a−1). Unlike the Arctic Ocean, there was no secular trend in either sea ice cover or annual primary production in the Southern Ocean during our 9-year study. Interannual variability in annual production was most closely tied to changes in sea ice cover, although changes in sea surface temperature also played a role. Only 31% of the variation in annual production was explained by the Southern Annular Mode. Annual primary production could increase in the future as stronger winds increase nutrient upwelling.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2007JC004551

Primary production in the Southern Ocean, 1997–2006

. PISCES-v2 (Pelagic Interactions Scheme for Carbon and Ecosystem Studies volume 2) is a biogeochemical model which simulates the lower trophic levels of marine ecosystems (phytoplankton, microzooplankton and mesozooplankton) and the biogeochemical cycles of carbon and of the main nutrients (P, N, Fe, and Si). The model is intended to be used for both regional and global configurations at high or low spatial resolutions as well as for short-term (seasonal, interannual) and long-term (climate change, paleoceanography) analyses. There are 24 prognostic variables (tracers) including two phytoplankton compartments (diatoms and nanophytoplankton), two zooplankton size classes (microzooplankton and mesozooplankton) and a description of the carbonate chemistry. Formulations in PISCES-v2 are based on a mixed Monod–quota formalism. On the one hand, stoichiometry of C / N / P is fixed and growth rate of phytoplankton is limited by the external availability in N, P and Si. On the other hand, the iron and silicon quotas are variable and the growth rate of phytoplankton is limited by the internal availability in Fe. Various parameterizations can be activated in PISCES-v2, setting, for instance, the complexity of iron chemistry or the description of particulate organic materials. So far, PISCES-v2 has been coupled to the Nucleus for European Modelling of the Ocean (NEMO) and Regional Ocean Modeling System (ROMS) systems. A full description of PISCES-v2 and of its optional functionalities is provided here. The results of a quasi-steady-state simulation are presented and evaluated against diverse observational and satellite-derived data. Finally, some of the new functionalities of PISCES-v2 are tested in a series of sensitivity experiments.

/pdf/pisces-v2-an-ocean-biogeochemical-model-for-carbon-and-4numeecyss.pdf

PISCES-v2: an ocean biogeochemical model for carbon and ecosystem studies

SeaWiFS was used to examine the spatial and temporal distribution of chlorophyll-a (chl-a) concentrations around the island of South Georgia during four summers between October 1997 and March 2001. A comparison was made between SeaWiFS and ship-collected (in situ) chl-a gathered during three of these seasons. A significant correlation was found between daily SeaWiFS and in situ match-ups (r2=0.62). At low chl-a concentrations ( 5 mg m−3). Analysis of SeaWiFS data from two survey boxes (the Western and Eastern Core Boxes) sampled during cruises indicated significant differences between seasons and regions; the 1999 and 2000 seasons were nearly twice as productive as the 1998 and 2001 seasons. In addition, phytoplankton biomass was significantly higher in the Western (∼1.4 mg m−3) than in the Eastern Core Box (∼0.6 mg m−3). These seasonal and regional differences also were reflected in the distribution of copepods, one of the major zooplankton groups around South Georgia. SeaWiFS revealed patterns of growth outside of the survey boxes and cruise periods (January only). Blooms regularly occurred to the southwest and directly north of the island, and occasionally occupied the entire area between South Georgia and the Polar Front. In addition, blooms took place any time between October and March but not continuously. Primary production at South Georgia is mainly a local feature with little growth initiated upstream. However, chl-a may remain elevated downstream of the island (∼40°W) as part of a continuous feature along the Polar Front to the 0° meridian. The passage of the Antarctic Circumpolar Current over the ridge and shelf waters in the vicinity of South Georgia may contribute micronutrients such as iron, and could partially explain the elevated chl-a levels associated with the island. We also examine the role of temperature, light and grazing on controlling phytoplankton productivity in this region of the Southern Ocean.

SeaWiFS in the southern ocean: spatial and temporal variability in phytoplankton biomass around South Georgia

During the austral summer of 2002, a large and persistent phytoplankton bloom was detected with SeaWiFS imagery in the Georgia Basin to the north-west of South Georgia, while waters to the east of the island were relatively unproductive. A British Antarctic Survey research cruise in January 2002 confirmed this west/east difference with production values of up to 2.5 g C m(-2) d(-1) and chlorophyll a (chl a) values up to 15 mg m(-3) at stations to the northwest of the island and 0.17 g C m(-2) d(-1) and 1.3 mg chl a m(-3) to the northeast. These differences were not attributable to light limitation as mixed layer depth never exceeded critical depth. Instead, substantial nutrient depletions to the northwest of the island compared with the northeast suggested a difference in nutrient use between the two regions. The exceedingly high nutrient depletions (to < 6.0 and 0.3 mmol m(-3) for NO3-N and PO4-P, respectively) measured to the northwest were associated with an anticyclonic eddy situated over the Northwest Georgia Rise. Furthermore, differences in NO3-N:PO4-P depletion ratios suggested a greater ability in the northwest phytoplankton to utilise NO3-N, and a greater dependence on NH4-N at the northeast stations. Three distinct station groups were identified around the island based on watermass and size-fractionated chlorophyll. To the east, waters were characterised by a high proportion of microplankton and low NO3-N:PO4-P depletion ratios, to the west, by either a high proportion of microplankton and high NO3-N:PO4-P depletion ratios, or a high proportion of nanoplankton and moderate NO3-N:PO4-P depletion ratios. We consider this to be indicative of greater Fe availability, promoting NO3-N use, to the northwest of South Georgia. However, an absence of microplankton over the western shelf regions may be due to size selective grazing by krill. Our field data, in conjunction with SeaWiFS imagery, indicated that the Georgia Basin phytoplankton most likely originated upstream of South Georgia. Subsequent interactions with the Northwest Georgia Rise and South Georgia's south-western shelf promoted increased growth that converged to the west of the island to form a large bloom in the Georgia Basin.

Contrasting primary production regimes around South Georgia, Southern Ocean: large blooms versus high nutrient, low chlorophyll waters

Data collected between 1926 and 1990, during the Discovery Investigations and fourteen subsequent cruises, have allowed the description of spatial and temporal variability of temperature, salinity, phosphate, silicate, nitrate and chlorophyll a in the surface waters around the subantarctic island of South Georgia. Measurements made in Antarctic Circumpolar Current water were compared with others made in Weddell Sea water, and profiles from shelf, shelf-slope and oceanic sites were considered separately. In summer, Weddell Sea surface water was significantly colder than that of the Antarctic Circumpolar Current (1.66 and 2.59°C, respectively), but no changes of temperature corresponded with bathymetry. There were no systematic differences between the salinity measurements made in Weddell Sea surface water and those in Antarctic Circumpolar Current water; however, oceanic waters were always more saline than those over the shelf-slope and shelf (33.91, 33.89 and 33.86, respectively). Silicate levels correlated well with seawater temperature, and Weddell Sea surface water concentrations were substantially higher than those of the Antarctic Circumpolar Current (51 and 25 mmol m−3, respectively, in winter; 29 and 13 mmol m−3 in summer). No such differences were found for phosphate or nitrate, and no systematic differences in any of the nutrient levels were attributable to bathymetry. Although summer chlorophyll a levels appeared to be highest in Antarctic Circumpolar Current water over the shelf and shelf-slope (2.7–3.0 mg m−3), no significant differences were attributable to water-mass or bathymetry. A clear seasonal pattern was evident, with the warmest seawater conditions, minimum nutrient concentrations and highest chlorophyll a levels found between December and March. Phosphate and nitrate were never exhausted: the lowest recorded phosphate concentrations were around 0.6 mmol m−3 and for nitrate 11 mmol m−3. However, low concentrations of silicate (∼ 1.0 mmol m−3) were evident during some summer surveys from the 1920s through to the present day. Average nutrient deficits calculated either between winter and summer mixed-layer concentrations, or between summer mixed-layer and Tmin values, produced similar estimates of carbon fixation for both phosphate and silicate, while nitrate appeared to underestimate carbon production. Phosphate and silicate deficits were considered to be satisfactory predictors of carbon production, which was about 30–40 g C m−2 year−1 in a mixed-layer depth of 50 m. Considerable interannual variability was found, with winter-like conditions prevailing until January on some occasions, and apparent year-to-year variability in the timing and magnitude of nutrient utilisation (especially silicate) by phytoplankton. A relationship was found between sea surface conditions around South Georgia in summer and the preceding winter's fast-ice duration at the South Orkney Islands, which implied that some of this variability was attributable to large-scale change over the Scotia Sea as a whole, as opposed to local influences.

Seasonal and annual change in seawater temperature, salinity, nutrient and chlorophyll a distributions around South Georgia, South Atlantic

Swarming is a fundamental part of the life of Euphausia superba, yet we still know very little about what drives the considerable variability in swarm shape, size and biomass. We examined swarms across the Scotia Sea in January and February 2003 using a Simrad EK60 (38 and 120 kHz) echosounder, concurrent with net sampling. The acoustic data were analysed through applying a swarm-identification algorithm and then filtering out all non-krill targets. The area, length, height, depth, packing-concentration and inter-swarm distance of 4525 swarms was derived by this method. Hierarchical clustering revealed 2 principal swarm types, which differed in both their dimensions and packing-concentrations. Type 1 swarms were generally small ( 100 km away from the next swarm). The distribution of swarm types over the survey grid was examined with respect to a number of potential explanatory variables describing both the environment and the internal-state of krill (namely maturity, body length, body condition). Most variables were spatially averaged over scales of similar to 100 km and so mainly had a mesoscale perspective. The exception was the level of light (photosynthetically active radiation (PAR)) for which measurements were specific to each swarm. A binary logistic model was constructed from four variables found to have significant explanatory power (P < 0.05): surface fluorescence, PAR, krill maturity and krill body length. Larger (type 2) swarms were more commonly found during nighttime or when it was overcast during the day, when surface fluorescence was low, and when the krill were small and immature. A strong pattern of diel vertical migration was not observed although the larger and denser swarms tended to occur more often at night than during the day. The vast majority of krill were contained within a minor fraction of the total number of swarms. These krill-rich swarms were more common in areas dominated by small and immature krill. We propose that, at the mesoscale level, the structure of swarms switches from being predominantly large and tightly packed to smaller and more diffuse as krill grow and mature. This pattern is further modulated according to feeding conditions and then level of light. (C) 2009 Elsevier Ltd. All rights reserved.

Variability and predictability of Antarctic krill swarm structure

Data from a variety of sources reveal a warm-core anticyclonic circulation above the Northwest Georgia Rise (NWGR), an similar to2000-m high bathymetric feature north of South Georgia. The sense of the circulation is opposite to the general cyclonic flow in the Georgia Basin. The circulation shows the characteristics of a stratified Taylor column: dimensional analysis shows that the local bathymetry and hydrography are conducive to the formation of such. ERS2 altimeter data show that the column, whilst not fully permanent, is nonetheless a recurring feature. High concentrations of chlorophyll-a are observed at the centre of the circulation, indicating that the modulation of the physical environment has significant consequences for the local biogeochemical system via enhanced primary production. Enhanced chlorophyll-a extends in a long plume from the NWGR along pathways indicated by drifters; this passive redistribution may have consequences for the larger (basin-) scale ecosystem.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2003GL018039

M. J. Whitehouse

Papers

SeaWiFS in the southern ocean: spatial and temporal variability in phytoplankton biomass around South Georgia

Contrasting primary production regimes around South Georgia, Southern Ocean: large blooms versus high nutrient, low chlorophyll waters

Seasonal and annual change in seawater temperature, salinity, nutrient and chlorophyll a distributions around South Georgia, South Atlantic

Variability and predictability of Antarctic krill swarm structure

An anticyclonic circulation above the Northwest Georgia Rise, Southern Ocean