Particulate organic matter in the coastal and estuarine waters of Goa and its relationship with phytoplankton production

In the coastal and estuarine waters of Goa, particulate organic carbon (POC) varied from 0.52 to 2.51 mg l^?1 and from 0.28 to 5.24 mg l^?1 and particulate phosphorus (PP) varied from 0.71 to 5.18 μg l^?1 and from 0.78 to 20.34 μg l^?1, respectively. The mean values of chlorophyll and primary productivity were 1.94 mg m^?3 and 938.1 mg C m^?2 day^?1 in the coastal waters and 4.3 mg m^?3 and 636.5 mg C m^?1 day^?1 in the estuarine waters, respectively.$\text{POC}\text{chl}$ ratios were low in June and October even when POC values were quite high. The POC in surface waters was linearly correlated with the chlorophyll content. Also PP increased when chlorophyll and primary productivity remained high. The results suggest that the phytoplankton was sharply increasing and contributed to POC and PP content. The percentage of detritus calculated from the intercept values of chlorophyll on POC varied from 46 to 76% depending on season. Results indicate that the major portion of POC and PP during postmonsoon (October–January) is derived from phytoplankton production while the allochthonous matter predominate during monsoon (June–September).     

Remote Sensing Observations of Ocean Surface Chlorophyll and Temperature with the Impact of Cyclones and Depressions over the Bay of Bengal Water

MODIS-Aqua derived eight-day composite chlorophyll concentration data analyzed to study the impact of cyclones and depressions on the Bay of Bengal productivity. A total of 15 cyclonic storms and depressions picked up from the India Meteorological Department datasets. MODIS-Aqua data analyzed during October 2002 to December 2009. There was observation of depressions (D), deep depressions (DD), cyclonic storms (CS), severe cyclonic storms (SCS), and very severe cyclonic storms (VSCS) with categories of intensities (“T” numbers 1.5–6) and wind speeds (25–108 knots). The chlorophyll concentration observed to be high (1.0–5.0 mg/m³) with the impact in the coastal and offshore waters. Quickscat scatterometer data showed high wind speed (about 10 meters/second). Sea surface temperature (SST) observed to be decreased (roughly 2°C) with effect of cyclones. The cyclone numbers, intensity, and chlorophyll concentration has been observed to be increasing from 2002 to 2009, with observation of VSCS “Sidr” during 2007. The study would be interesting to link carbon flux/sequestration, marine food chain, and harnessing fishery resources in a postcyclone period.     

Remote Sensing of Chlorophyll and Sea Surface Temperature in Indian Water with Impact of 2004 Sumatra Tsunami

The daily and weekly averaged Indian Remote Sensing satellite IRS-P4 Ocean Color Monitor (OCM) derived chlorophyll images were generated and interpreted in terms of pretsunami, tsunami, and posttsunami periods in the Bay of Bengal and Andaman Sea. There has been observation of increase in chlorophyll concentration up to 5.0 mg/m3 in the tsunami-affected coastal waters. The high chlorophyll concentration lasted for about one week after the tsunami catastrophe. The standard deviation for different transects in the tsunami-affected water were plotted. The high chlorophyll has been observed for selected transects in the aftermath of the tsunami event in coastal regions, and offshore water has also shown increase in chlorophyll concentration (～1.0 mg/m3) in the Bay of Bengal. The analysis indicated that the tsunami waves might have displaced and spread the high chlorophyll coastal water towards offshore. NASA Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua daytime sea surface temperature (SST) daily images were retrieved and displayed during December 21, 2004, to January 6, 2005, and indicated the cooling (0.5–1°C) in the Bay of Bengal around Tamil Nadu and Andhra coast. The National Oceanographic and Atmospheric Prediction-National Center for Environment Prediction (NOAA-NCEP) data for five weeks (December 9, 2004–January 12, 2005) were retrieved to study the SST variability trend in prior to MODIS data and indicated 0.5–1°C cooling of the Bay of Bengal water off Kakinada, Chennai, Cuddalore, and Nagapattinam region on December 26 and 28, 2004.     

Biological Characteristics of Central Indian Basin Waters During the Southern Summer

Phytoplankton biomass, taxonomy, primary productivity, and photosynthetically available radiation (PAR) were studied as part of baseline data collection for prospective nodule mining in the Central Indian Basin during the ORV Sagar Kanya cruise SK-120 in January 1997. The phytoplankton cell counts and chlorophyll a estimates showed low biomass level, suggesting low rates of primary productivity in the region studied. The average chlorophyll a value was 0.775 mg m^?3 at surface and 17.75 mg m^?2 in the water column. Similarly, average primary productivity at surface was 3.72 mg C m^?3 d^?1 and was 51.23 mg C m^?2 d^?1 in column. The chlorophyll a maxima at 50 to 80 m was the characteristic feature of the euphotic zones of the area. Average phytoplankton counts at the surface were low (3960 cells/l), compared to those at 25 m (6421 cells/l) and 75 m (5187 cells/l). At most of the stations mesozooplankton biomass was maximum in the top 50 m water column, indicating the importance of grazing in the euphotic zone. Appreciable quantities of mesozooplankton were observed below the euphotic zone, where settlement of chlorophyll a occurs. The low iron concentration in the water and its relationship with the water column productivity were correlated. The results show that waters in the CIB have low productivity in the surface as well as subsurface layers. This is expected to change in this case of a mining discharge in to these layers, possibly locally affecting the existing marine ecosystems. The final impact of such mining activity may remain negligible in the deep sea environment.     

Dynamic patterns of dissolved nitrogen in the Southern Bight of the North Sea

Spatial and temporal variations of dissolved inorganic nitrogen (DIN) have been assessed in onshore and offshore areas of the Southern Bight on the basis of several years' measurements. They indicate that both the residual flow lines and DIN isoconcentration lines run parallel with the coast except in the vicinity of important freshwater discharge points such as the Scheldt estuary. Evidence was found that the seasonal DIN oscillations are not created through fluctuations in input conditions at the lateral boundaries, despite considerable fluctuations in these inputs which include the English Channel (from 500 tons(t) N day^?1 in June up to approximately 2000 t N day^?1 in February) and also rivers such as the Scheldt estuary (up to 50 t N day^?1 in January but less than 5 t N day^?1 in June–July). In both the onshore and offshore areas the sum of daylight phytoplanktonic nitrogen intake and sediment release of nitrogen corresponds to the observed DIN variations during most of the year. Pelagic N-mineralization from natural or grazing mortality of phytoplankton (220 mg N m^?2 day^?1 onshore at its maximum) can account for the differences (200 mg N m^?2 day^?1 onshore at its maximum), especially at the end of the phytoplankton spring bloom. Although the causes of DIN oscillations onshore and offshore are the same, the results differ because offshore (1) the vegetative season lasts longer, and (2) DIN is exhausted at the end of the phytoplankton spring bloom.     

Euphausiid population structure and grazing in the Antarctic Polar Frontal Zone — austral autumn 2004

The euphausiid community structure and grazing dynamics were investigated in the West Indian sector of the Polar Frontal Zone during the austral autumn 2004. Subsurface (200m) temperature profiles indicated that an intense frontal feature, formed by the convergence of the Subantarctic Front and the Antarctic Polar Front bisected the survey area into two distinct zones, the Subantarctic Zone (SAZ) and the Antarctic Zone (AAZ). Total integrated chlorophyll a (Chl a) biomass was typical for the region (<25mg Chl a m^?2), and was dominated by picophytoplankton. Total euphausiid abundance and biomass ranged from 0.1 m^?3 to 3.1 m^?3 and from 0.1mg dry weight m^?3 to 8.1mg dry weight m^?3 respectively, and did not differ significantly between the stations occupied in the SAZ and AAZ (p > 0.05). A multivariate analysis identified two interacting mechanisms controlling the distribution patterns, abundance and biomass of the various euphausiid species, namely (1) diel changes in abundance and biomass, and (2) restricted distribution patterns associated with the different water masses. Ingestion rates were determined for five euphausiid species. Euphausia triacantha had the highest daily ingestion rate, ranging from 1 226.1ng pigment (pigm) ind^?1 day^?1 to 6 029.1ng pigm ind^?1 day^?1, whereas the lowest daily ingestion rates were observed in the juvenile Thysanoessa species (6.4–943.0ng pigm ind^?1 day^?1). The total grazing impact of selected euphausiids ranged from <0.1μg pigm m^?2 day^?1 to 20.1μg pigm m^?2 day^?1, corresponding to <0.15% of the areal Chl a biomass. The daily ration estimates of autotrophic carbon for the euphausiids suggest that phytoplankton represent a minor component in their diets, with only the sub-adult E. vallentini consuming sufficient phytoplankton to meet their daily carbon requirements.     

Productivity of dinoflagellate blooms on the west coast of South Africa,as measured by natural fluorescence

The biomass and productivity of phytoplankton populations inshore on the west coast of South Africa were investigated towards the end of the upwelling season, a period when high-biomass dinoflagellate blooms are common. Productivity was estimated from natural fluorescence measurements (P_NF ), using photosynthesis (P) v. irradiance (E) relationships (P_E ) and by means of the in situ ¹⁴C-method (P_C ) A linear regression of P_NF productivity against P_C and P_E productivities yielded a slope of 0.911 and an r ₂ of 0.83 (n = 41). Physical and biological variability was high inshore, reflecting alternating periods of upwelling and quiescence. Mean chlorophyll inshore (within a 12 m water column) ranged from 0.7 to 57.8 (mean = 8.9) mg·m^&minus3, mean P_NF productivity ranged from 8.4 to 51.0 (mean = 24.6) mgC·m^?3·h^?1 and daily integral P_NF productivity from 0.8 to 4.8 (mean = 2.3) gC·m^?2·day^?l. Transects sampled during active and relaxation phases of upwelling had different chlorophyll distributions. High chlorophyll concentrations (sometimes >50 mg·m^?3) were associated with surface blooms within the region of the upwelling front. Estimates of daily water-column P_NF productivity within these frontal blooms ranged from 4.0 to 5.6 gC·m^?2·day^?1. With relaxation of wind stress, blooms dominated by dinoflagellates flooded shorewards and often formed red tides. Chlorophyll concentrations of > 175 mg·m^?3 and productivity rates > 500 mgC·m^?3·h^?1 and 12 gC·m^?2·day^?1 were measured during a particularly intense red tide. Offshore, the water column was highly stratified with a well-defined subsurface chlorophyll maximum layer within the pycnocline region. Estimates of daily water-column P_NF productivity ranged from 2.4 to 4.0 gC·m^?2·day^?1 offshore. The high productivity of shelf waters on the West Coast in late summer can be ascribed largely to dinoflagellate populations and their success in both upwelling systems and stratified conditions.     

Factors controlling the timing of major spring bloom events in an UK south coast estuary

Factors controlling the timing of major (>10 mg chlorophyll a m⁻³) spring bloom events in the estuarine waters of the Solent, on the south coast of the UK, have been investigated. Winter to summer variations in chlorophyll a concentration together with relevant meteorological and hydrographical data have been analysed for 5 years (1988, 1992, 2001, 2002 and 2003). Mean water column irradiance is demonstrated to be the main factor controlling the timing of the first major spring bloom event, usually dominated by large chain-forming diatoms. When chlorophyll a concentration first exceeds 10 mg m⁻³ in spring (usually in May) the mean water column photosynthetic active radiation (PAR) averaged for one week prior to the sampling date was always >380 W h m⁻² d⁻¹. Prior to the main spring bloom event surface incident radiation and water turbidity combine to limit chlorophyll a concentration to levels <10 mg m⁻³. Chlorophyll a concentrations >10 mg m⁻³ do not occur in the Solent until almost the entire 10 m water column is within the euphotic zone (i.e. above 1% light level) and light extinction coefficient (k) is ca. ≤0.5 m⁻¹. Statistically, river flow explains the largest percentage of the variations in k and the delayed bloom in June 2002 is due to increased cloud cover and high levels of rainfall in May, which caused a reduction in surface incident irradiance and increased turbidity. Chlorophyll a peaks during these major bloom events generally occur on spring tides when increased mixing rates favour net growth of diatoms.     

Satellite-derived measurements of spatial and temporal chlorophyll-a variability in Funka Bay, southwestern Hokkaido, Japan

Chlorophyll-a (chl-a) concentration has an important economic effect in coastal and marine environments on fisheries resources and marine aquaculture development. Monthly climatologies the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) derived chl-a from February 1998 to August 2004 around Funka Bay were used to investigate the spatial and temporal variability of chl-a concentrations. SeaWiFS-derived suspended sediment, MODIS derived sea surface temperature (SST), solar radiation and wind data were also analyzed. Results showed two distinct chlorophyll blooms in spring and autumn. Chl-a concentrations were relatively low (<0.3 mg m⁻³) in the bay during summer, with high concentrations occurring along the coast, particularly near Yakumo and Shiraoi. In spring, chl-a concentrations increased, and a large (>2 mg m⁻³) phytoplankton bloom occurred. The spatial and temporal patterns were further confirmed by empirical orthogonal function (EOF) analysis. About 83.94% of the variability could be explained by the first three modes. The first chl-a mode (77.93% of the total variance) explained the general seasonal cycle and quantified interannual variability in the bay. The spring condition was explained by the second mode (3.89% of the total variance), while the third mode (2.12% of the total variance) was associated with autumn condition. Local forcing such as the timing of intrusion of Oyashio water, wind condition and surface heating are the mechanisms that controlled the spatial and temporal variations of chlorophyll concentrations. Moreover, the variation of chlorophyll concentration along the coast seemed to be influenced by suspended sediment caused by resuspension or river discharge.     

Photoadaptation of carboxylating enzymes and photosynthesis during a spring bloom

Properties of the light saturation curve of photosynthesis and ribulose-1,5-bisphosphate carboxylase (RuBPC) activity are shown to change qualitatively in a natural population of marine phytoplankton during a spring bloom. Evidence is presented to show that these changes constitute photoadapative responses to increasing irradiance. As irradiance increased during the bloom, both the level of light-saturated photosynthesis (P_m) and the initial slope of the light saturation curve (α = photosynthetic efficiency) increased whether those parameters were normalized to chlorophyll a concentration (P_m^b, α^b) or to cell numbers (P_m^c, α^c). The magnitudes of these changes were such that I_k (= P_m/α, the photoadaptation parameter) did not change, but I_m, the light intensity at which photosynthesis becomes saturated, increased. RuBPC activity, both chlorophyll a (RuBPC^b) and cell number normalized (RuBPC^c), also increased during the bloom. We suggest that these adaptations were achieved by simultaneously increasing the number of photosynthetic units, proportionately decreasing the photosynthetic unit size, and increasing both the concentrations of the enzymes of the dark reactions and possibly also of photosynthetic electron transport components.We also observed diminished levels of photoinhibition in the high light adapted cells late in the bloom and have suggested that this was a consequence of the same suite of physiological changes.In situ carbon fixation per cell increased during the bloom whereas no change occurred in this parameter when normalized to chlorophyll a concentration. Although these photoadaptive responses thus permitted carbon to be fixed in situ more rapidly per cell, at a constant efficiency with respect to investment of energy in the photosynthetic apparatus, they did not result in a change in growth rate. Based on consideratios of the role of time scale in physiological adaptation, however, it is suggested that the observed alterations in photosynthesis with increasing irradiance might permit a cell to more rapidly fill an energy quota for division, possibly an advantage in a mixing environment in which energy is patchily distributed, both spatially and temporalyy.Phosphoenolpyruvate carboxylase activity when normalized to chlorophyll a (PEPC^b) did not change during the bloom while chlorophyll a normalized dark carbon fixation decreased sharply and was quantitatively small compared to PEPC^b. On this basis and considering that RuBPC^b increased during the bloom, it is suggested that, although PEPC may be involved in dark carbon fixation, its most important quantitative role is probably an indirect one in light dependent photosynthesis.We have also considered the relevance of laboratory results on photoadaptation to interpretations of field studies and have suggested that batch culture studies must be treated with caution but that turbidistat and semi-continuous methods provide reasonable simulations of natural conditions.     

Short-term variability of suspended sediment and phytoplankton in Tampa Bay,Florida: Observations from a coastal oceanographic tower and ocean color satellites

We examined short-term phytoplankton and sediment dynamics in Tampa Bay with data collected between 8 December 2004 and 17 January 2005 from optical, oceanographic, and meteorological sensors mounted on a coastal oceanographic tower and from satellite remote sensing. Baseline phytoplankton (chlorophyll-a, Chl) and sediment concentrations (particle backscattering coefficient at 532 nm, bbp(532)) were of the order of 3.7 mg m⁻³ and 0.07 m⁻¹, respectively, during the study period. Both showed large fluctuations dominated by semidiurnal and diurnal frequencies associated with tidal forcing. Three strong wind events (hourly averaged wind speed >8.0 m s⁻¹) generated critical bottom shear stress of >0.2 Pa and suspended bottom sediments that were clearly observed in concurrent MODIS satellite imagery. In addition, strong tidal current or swells could also suspend sediments in the lower Bay. Sediments remained suspended in the water column for 2–3 days after the wind events. Moderate Chl increases were observed after sediment resuspension with a lag time of ˜1–2 days, probably due to release of bottom nutrients and optimal light conditions associated with sediment resuspension and settling. Two large increases in Chl with one Chl > 12.0 mg m⁻³ over ˜2 days, were observed at neap tides. For the study site and period, because of the high temporal variability in phytoplankton and sediment concentrations, a monthly snapshot can be different by −50% to 200% from the monthly “mean” chlorophyll and sediment conditions. The combination of high-frequency observations from automated sensors and synoptic satellite imagery, when available, is an excellent complement to limited field surveys to study and monitor water quality parameters in estuarine environments.     

Evidence for the grazing hypothesis: Grazing reduces phytoplankton responses of the HNLC ecosystem to iron enrichment in the western subarctic pacific (SEEDS II)

A mesoscale iron-enrichment study (SEEDS II) was carried out in the western subarctic Pacific in the summer of 2004. The iron patch was traced for 26 days, which included observations of the development and the decline of the bloom by mapping with sulfur hexafluoride. The experiment was conducted at almost the same location and the same season as SEEDS (previous iron-enrichment experiment). However, the results were very different between SEEDS and SEEDS II. A high accumulation of phytoplankton biomass (∼18 mg chl m⁻³) was characteristic of SEEDS. In contrast, in SEEDS II, the surface chlorophyll-a accumulation was lower, 0.8 to 2.48 mg m⁻³, with no prominent diatom bloom. Photosynthetic competence in terms of F _v/F _m for the total phytoplankton community in the surface waters increased after the iron enrichments and returned to the ambient level by day 20. These results suggest that the photosynthetic physiology of the phytoplankton assemblage was improved by the iron enrichments and returned to an iron-stressed condition during the declining phase of the bloom. Pico-phytoplankton (<2 μm) became dominant in the chlorophyll-a size distribution after the bloom. We observed a nitrate drawdown of 3.8 μM in the patch (day 21), but there was no difference in silicic acid concentration between inside and outside the patch. Mesozooplankton (copepod) biomass was three to five times higher during the bloom-development phase in SEEDS II than in SEEDS. The copepod biomass increased exponentially. The grazing rate estimation indicates that the copepod grazing prevented the formation of an extensive diatom bloom, which was observed in SEEDS, and led to the change to a pico-phytoplankton dominated community towards the end of the experiment.     

A phytoplankton class-specific primary production model applied to the Kerguelen Islands region (Southern Ocean)

As part of the KErguelen: compared study of the Ocean and the Plateau in Surface water (KEOPS) project in late summer 2005, we examine the phytoplankton community composition and associated primary production in the waters surrounding the Kerguelen Archipelago, with the emphasis on two contrasted environments: (i) the Kerguelen Plateau, where a large bloom occurs annually, and (ii) the high-nutrient low-chlorophyll (HNLC) offshore waters. A biomarker pigment approach was used to assess the community composition in terms of chlorophyll biomass of three phytoplankton size classes, namely micro-, nano-, and picophytoplankton. The second objective was to evaluate a global class-specific approach for estimating the contribution of the three pigment-based size classes to the primary production in the study area. To do so, primary production rates associated with each phytoplankton class were computed from the class-specific chlorophyll biomass coupled to a class-specific primary production model, and compared with in situ measurements of size-fractionated ¹³C-based primary production. The iron-enriched bloom region was dominated by microphytoplankton (diatoms), which contributed 80–90% to the total primary production (of ≈1 g C m^?2 d^?1). In the HNLC area, the primary production was about 0.30 g C m^?2 d^?1, mainly (65%) achieved by small diatoms and nanoflagellates. The model results show a good overall agreement between predicted and measured total primary production rates. In terms of size classes, agreements were higher for the bloom region than for the HNLC waters. Discrepancies in this complex iron-limited area may be explained essentially by the smaller size of diatoms, or a different set of photophysiological properties.     

Plankton productivity and biomass in a tributary of the upper Chesapeake Bay. I. Importance of size-fractionated phytoplankton productivity,biomass and species composition in carbon export

Phytoplankton productivity, community composition and biomass were determined over a nine-month period in brackish waters of the lower Gunpowder River, a tributary of Chesapeake Bay. Primary productivity followed expected seasonal magnitudes for temperate estuaries with rates exceeding 142·4 mg C m^?3 h^?1 in July through September 1979 and minimum rates of 1·6 mg C m^?3 h^?1 in February 1980. Annual primary production was estimated at 45·5 gC m^?2. Cell numbers were highest in August, September and November with cyanophytes dominating the planktonic algae. Primary productivity, chlorophyll concentrations and cell densities were dominated by nanoplanktonic forms (< 10 μm) through-out the study. Phytoplankton carbon calculated from cells volumes exceeded nutritional requirements of the pelagic herbivores in all months suggesting a mean daily export (to the bay or sediments) of 1607 mg C m^?3 d^?1.     

Identification and classification of vertical chlorophyll patterns in the Benguela upwelling system and Angola-Benguela front using an artificial neural network

Information on the vertical chlorophyll structure in the ocean is important for estimating integrated chlorophyll a and primary production from satellite. For this study, vertical chlorophyll profiles from the Benguela upwelling system and the Angola-Benguela front were collected in winter to identify characteristic profiles. A shifted Gaussian model was fitted to each profile to estimate four parameters that defined the shape of the curve: the background chlorophyll concentration (B ₀), the height parameter of the peak (h), the width of the peak (σ) and the depth of the chlorophyll peak (z_m ). A type of artificial neural network called a self-organizing map (SOM) was then used on these four parameters to identify characteristic profiles. The analysis identified a continuum of chlorophyll patterns, from those with large surface peaks (>10 mg m^?3) to those with smaller near-surface peaks (<2 mg m^?3). The frequency of occurrence of each chlorophyll pattern identified by the SOM showed that the most frequent pattern (～12%) had a near-surface peak and the least frequent pattern (～2%) had a large surface peak. These characteristic profile shapes were then related to pertinent environmental variables such as sea surface temperature, surface chlorophyll, mixed layer depth and euphotic depth. Partitioning the SOM output map into environmental categories showed large peaks of surface chlorophyll dominating in water with cool temperature, high surface chlorophyll concentration and shallow mixed layer and euphotic depth. By contrast, smaller peaks of subsurface chlorophyll were in water with warmer temperature, lower surface chlorophyll concentration, intermediate mixed layer and deep euphotic depth. These relationships can be used semi-quantitatively to predict profile shape under different environmental conditions. The SOM analysis highlighted the large variability in shape of vertical chlorophyll profiles in the Benguela. This suggests that an ideal typical chlorophyll profile, as used in the framework of biogeochemical provinces, may not be applicable to this dynamic upwelling system.     

Spatial variability of the primary production and chlorophyll <Emphasis Type="Italic">a</Emphasis> concentration in the drake passage in the austral spring

The spatial distribution of the primary production (PP) and the chlorophyll a concentration (Chl) were investigated during two research cruises in the Drake Passage area in October–November of 2007 and 2008. The algorithm evaluating the integral PP (PP_int) for the water column in this area was developed based on the data on the surface chlorophyll (Chl_s) and the incident solar irradiance obtained in 2004–2008 in the Atlantic Sector of the Southern Ocean. The results obtained both by the experimental and model approaches suggested that the Polar Front (PF) region of the Drake Passage was characterized by low values of both the PP_int (<100 mg C/m² per day) and Chl_s (0.08–0.20 mg/m³) in October–November. Low values of the Chl_s and relatively high phaeophytine a concentrations indicated the winter succession state of the phytoplankton community in the Antarctic Ocean and the southern Polar Frontal Zone (PFZ). The seasonal warming of the surface water layers and the developing pycnocline resulted in a phytoplankton bloom and a Chl_s concentration of more than 1 mg/m³ in mid-November in this area and the Subantarctic waters.     

Phytoplankton production characteristics in the southern Atlantic and the Atlantic sector of the Southern Ocean in the austral summer of 2009–2010

In December–January of 2010 the spatial distribution of the phytoplankton production characteristics was studied along transects in the vicinity of the Greenwich meridian (I) and in the Drake Passage (II). On transect I, the surface chlorophyll a concentration and primary production varied from 0.11 up to 3.57 mg/m³ and from 4.38 up to 37.47 mgC/m³ per day, respectively. The chlorophyll a in the photosynthetic layer and the integrated primary production varied from 10.7 up to 66.1 mg/m² and from 83 to 646 mgC/m² per day, respectively. On transect II in the surface layer, the chlorophyll a concentration changed within the range of 0.09–1.02 mg/m³ and the primary production ranged from 2.08 to 9.49 mgC/m³. The integrated values ranged from 6.32 to 38.29 mg/m² and from 41 to 221 mgC/m² per day, respectively. The moderate means of themaximum quantum yield (F _v/F _m) on transects I and II (0.41 and 0.35, respectively) testify to the low activity of the phytoplankton’s photosynthetic apparatus. The studied water areas in the Southern Ocean differed both in the phytoplankton biomass expressed in the chlorophyll a concentration values and in the conditions of the primary production formation.     

Silicon dynamics within an intense open-ocean diatom bloom in the Pacific sector of the Southern Ocean

An intense diatom bloom developed within a strong meridional silicic acid gradient across the Antarctic Polar Front at 61°S, 170°W following stratification of the water column in late October/early November 1997. The region of high diatom biomass and the silicic acid gradient propogated southward across the Seasonal Ice Zone through time, with the maximum diatom biomass tracking the center of the silicic acid gradient. High diatom biomass and high rates of silica production persisted within the silicic acid gradient until the end of January 1998 (ca. 70 d) driving the gradient over 500 km to the south of its original position at the Polar Front. The bloom consumed 30 to >40 μM Si(OH)₄ in the euphotic zone between about 60 and 66°S leaving near surface concentrations <2.5 μM and occasionally <1.0 μM in its wake. Integrated biogenic silica concentrations within the bloom averaged 410 mmol Si m⁻² (range 162–793 mmol Si m⁻²). Average integrated silica production on two consecutive cruises in December 1997 and January 1998 that sampled the bloom while it was well developed were 27.5±6.9 and 22.6±20 mmol Si m⁻² d⁻¹, respectively. Those levels of siliceous biomass and silica production are similar in magnitude to those reported for ice-edge diatom blooms in the Ross Sea, Antarctica, which is considered to be among the most productive regions in the Southern Ocean. Net silica production (production minus dissolution) in surface waters during the bloom was 16–21 mmol Si m⁻² d⁻¹, which is sufficient for diatom growth to be the cause of the southward displacement of the silicic acid gradient. A strong seasonal change in silica dissolution : silica production rate ratios was observed. Integrated silica dissolution rates in the upper 100–150 m during the low biomass period before stratification averaged 64% of integrated production. During the bloom integrated dissolution rates averaged only 23% of integrated silica production, making 77% of the opal produced available for export to depth. The bloom ended in late January apparently due to a mixing event. Dissolution : production rate ratios increased to an average of 0.67 during that period indicating a return to a predominantly regenerative system.Our observations indicate that high diatom biomass and high silica production rates previously observed in the marginal seas around Antarctica also occur in the deep ocean near the Polar Front. The bloom we observed propagated across the latitudinal band overlying the sedimentary opal belt which encircles most of Antarctica implying a role for such blooms in the formation of those sediments. Comparison of our surface silica production rates with new estimates of opal accumulation rates in the abyssal sediments of the Southern Ocean, which have been corrected for sediment focusing, indicate a burial efficiency of 4.6% for biogenic silica. That efficiency is considerably lower than previous estimates for the Southern Ocean.     

Satellite and ship observations of Kuroshio warm-core ring 93A off Sanriku, northwestern North Pacific, in spring 1997

Synoptic ship and satellite observations were performed of the Kuroshio warm-core ring (KWCR) 93A and its adjacent waters, off Sanriku, northwestern North Pacific, between early April and late June 1997. The temporal and spatial distribution of chlorophylla (Chl-a) and sea surface temperature in the study area were analyzed using data from ADEOS Ocean Color and Temperature Scanner (OCTS) and NOAA Advanced Very High Resolution Radiometer (AVHRR). The objective of this study was to describe the temporal and spatial variability of the spring bloom and understand its relationship with the changes in the hydrographic structure of these waters in and around KWCR 93A. The maximum value of Chl-a concentration in the ring was less than 1 mg/m³ during April. The spring bloom in the ring occurred early in May and the relatively high maximum (>1.0 mg/m³) continued from early in May to mid-June. In late June, a ship-observed surface Chl-a concentration of less than 0.4 mg/m³ suggests that the spring bloom had already declined in and around KWCR 93A. Double spiral structures of warm and cold streamers appeared from late April to mid-May, which may have an influence on the occurrence of the spring bloom in and around the ring. In this episodic event, the warm streamer can maintain the available potential energy of the ring and the strength of upwelling around the ring. The cold streamer provided water with a high Chl-a concentration to the surface layer of the ring. In order to understand the temporal and spatial variability of Chl-a distribution in the ring, the behavior of the warm and cold streamers needs to be taken into consideration.     

Limnology of Lake Rotokawa and its outlet stream

Abstract

The water chemistry, flora, and fauna of Lake Rotokawa (38° 37.8’ S, 176° 11.2'E) was studied in 1975–76. The mean pH is 2.1 and thermal inflows may elevate the mean summer temperature of the surface waters 4.2°c above that of nearby cold water Lake Rotongaio (18.9°c). The temperature range of surface water was from 10.1 °c in winter to 23.1°c in summer. The major anions were SO₄ ^2? 679 g.m^?3, and Cl‐ 314 g.m^?3. Mean concentrations of major cations were Na⁺ 224 g.m^?3, K⁺ 28.9 g.m^?3, Ca²⁺ 13.3 g.m^?3, and Mg²⁺ 2.6 g.m^?3.

Two species of flagellate algae were recorded, of which Euglena anabaena was predominant. Only two benthic macroinvertebrates were found, larvae of Chironomus zealandicus, mean density 253 per square metre, and Helobdella sp., 1.3 per square metre.

The Parariki Stream was influenced by thermal springs in its upper and lower reaches, being cooler (24–25°c) about halfway along its length than near its source (27.8–39.0°c) or confluence (26.5°‐28.0°c) with the Waikato River. In the cooler stretch of the stream where unidentified benthic algae were not limited by high temperature, chlorophyll and total pigment increased from 3.9 to 377.9 mg.m^?3 and from 17.5 to 534.4 mg.m^?3 respectively, and nutrient levels fell (NO₃‐N, 22–10.5 mg.m^?3; NH₄‐N, 6440–230 mg.m^?3; and PO₄‐P, 51–19 mg.m^?3).