Moderate resolution satellite imagery was combined with in-situ observations of suspended sedimen... more Moderate resolution satellite imagery was combined with in-situ observations of suspended sediment flux from the Sacramento-San Joaquin River Delta to gain an understanding of event-scale suspended sediment budgets for San Francisco Bay. The event-scale budgets estimated were dependent on tidal conditions, duration of the highflow event, and the timing of the remote observation during the high-flow event. The exported fraction of suspended material entering the Bay from the Delta during high-flow conditions was greatest during ebb tides. Short, storm-driven high-flow events exported a larger fraction of their suspended sediment load than did longer-duration high-flow events such as spring snowmelts. The dependence of the event-scale budgets on environmental and meteorological conditions, combined with the lack of site-specific algorithms for estimating suspended sediment concentrations from remote observations, rendered inconclusive our attempts to develop a 'rule-of-thumb' regarding the fraction of sediment influx from large storms that passes through the system. It is possible that sitespecific algorithms and an increased sample size (i.e., more remote observations) combined with in-situ observations of sediment fluxes through the Golden Gate would improve the ability of the methods presented here to develop such a 'rule-of-thumb.'
The pelagic ecosystem of the open part of the Black Sea was analyzed from the point of view of it... more The pelagic ecosystem of the open part of the Black Sea was analyzed from the point of view of its temporal changes on interannual and seasonal basis. The material was collected during interdisciplinary expeditions to the Black Sea, between 1978–1996. The observed interannual variability is discussed for all plankton groups except protozooplankton. During 1980–1993 a gradual decrease of mean air temperature in winter and an increase in phytoplankton biomass in summer were observed. The lowest and the highest phytoplankton biomasses corresponded to high and low temperatures in 1980 and 1992 respectively. The climatic quasi-periodic 20-years oscillations of winter air temperature determine the general intensity of Black Sea current system and, as a result, favorable conditions for growth of phytoplankton. The analysis of historical phytoplankton data corroborates this hypothesis. According to surface chlorophyll “a” satellite measurements the interannual variations were seen in winter and spring during the period from 1978 to 1986.
The data on taxonomic composition, abundance, and biomass of phytoplankton and chlorophyll a conc... more The data on taxonomic composition, abundance, and biomass of phytoplankton and chlorophyll a concentration in the eastern part of the Mediterranean Sea during late summer period are given in the paper. Different methods of measurements of the chlorophyll a concentration are compared. All the quantitative characteristics of phytoplankton manifest the oligotrophic level of water productivity during the period under study. The spatial distribution of the abundance and biomass of phytoplankton and chlorophyll a concentration are significantly influenced by the mesoscale eddies of typical size 10-50 miles. The quantitative characteristics of phytoplankton in the coastal zone were usually higher, as compared with the open sea regions. As for vertical distribution of micro- and nanophytoplankton, the maximum cell concentrations occurred within the upper homogenous layer and in the layer of pycnocline. The vertical profiles of phytoplankton and chlorophyll a were compared with the profiles of fluorescence; the maximum of fluorescence corresponded to the maximum of chlorophyll a concentration and seemed to result from high concentration of picophytoplankton. The maximum of fluorescence also manifested itself in the cases when the cell densities in the layers of maximum if micro- and nanophytoplankton exceeded 104 cells per liter.
The pelagic ecosystem of the open part of the Black Sea is analyzed from the point of view of its... more The pelagic ecosystem of the open part of the Black Sea is analyzed from the point of view of its sustainability. The peculiarities of plankton community in the temperate region result in regular seasonal oscillations of high range, the biomass values varying 5–10 times during the year. In the coastal regions of the Black Sea the values of primary production, chlorophyll concentration, phyto- and zooplankton biomasses change according to typical pattern of seasonal variations of temperate and subtropical areas: spring bloom of phytoplankton is followed by its decrease due to both depletion of nutrients and grazing by herbivorous zooplankton in summer. At the same time in the open regions the bloom of phytoplankton occurs during winter, because in the cyclonic gyres main pycnicline rises into euphotic zone (so-called “Black-Sea upwelling”). Besides regular seasonal variations, long term interannual variations also take place. The evident example of such kind of changes is the pattern of fluctuations of phytoplankton biomass, that oscillates inversely to average air temperature in winter. Another example is the development of newcomer ctenophore Mnemiopsis leidyi in late 1980s, resulting in sharp decrease of zooplankton biomass. During previous decade mass development of jelly-fish Aurelia aurita took place. Taxonomic composition of phyto- and zooplankton also changes in response to influence outside.
The remote sensing data obtained by Coastal Zone Color Scanner (CZCS) on the satellite “Nimbus-7”... more The remote sensing data obtained by Coastal Zone Color Scanner (CZCS) on the satellite “Nimbus-7” collected during the period from 1978 to 1986 were used to analyse the seasonal variation of surface plant pigments distribution in the Black Sea, presented here on maps for each climatological month. The pattern of seasonal variations is typical for subtropical regions rather than for the temperate ones. The range of the absolute value of plant pigment surface concentration measured by remote sensing does not differ greatly from the values measured by direct methods.
A series of infrared NOAA satellite images of the northwestern Black Sea (resolution 1 km) and co... more A series of infrared NOAA satellite images of the northwestern Black Sea (resolution 1 km) and corresponding maps of chlorophyll “a” (SeaWiFS data, resolution 9 km) are analyzed for the period 1 June-28 August 1998. A major objective was detection of the movement of three synoptic-scale anticyclonic eddies over the continental slope and the entrainment of photopigment-rich coastal waters by them. The study examines the effects of wind direction on the visibility of eddies in the chlorophyll field, and attempts to identify conditions favoring the transport of chlorophyll-rich shelf waters into the sea's abyssal basin.
The annual cycle of the plankton dynamics in the central Black Sea is studied by a one‐dimensiona... more The annual cycle of the plankton dynamics in the central Black Sea is studied by a one‐dimensional vertically resolved physical‐biological upper ocean model, coupled with the Mellor‐Yamada level 2.5 turbulence closure scheme. The biological model involves interactions between the inorganic nitrogen (nitrate, ammonium), phytoplankton and herbivorous zooplankton biomasses, and detritus. Given a knowledge of physical forcing, the model simulates main observed seasonal and vertical characteristic features, in particular, formation of the cold intermediate water mass and yearly evolution of the upper layer stratification, the annual cycle of production with the fall and the spring blooms, and the subsurface phytoplankton maximum layer in summer, as well as realistic patterns of particulate organic carbon and nitrogen. The computed seasonal cycles of the chlorophyll and primary production distributions over the euphotic layer compare reasonably well with the data. Initiation of the spring...
A wealth of historical coastal water pH data has been collected using potentiometric glass electr... more A wealth of historical coastal water pH data has been collected using potentiometric glass electrodes, but the accuracy and stability of these sensors is poorly understood. Here we compared pH measurements from five potentiometric sensors incorporated into profiling Sea-Bird instrument packages and compared them to spectrophotometric measurements on discrete bottle samples collected at two to three depths associated with each cast. Differences ranged from 20.509 to 10.479 with a mean difference of 20.055 pH units. Ninety-two percent of the measurements were within60.2 pH units, but 1% of the measurements had differences greater than 0.322. Sensor performance was affected by depth, but most of the difference was associated with calibration shortcomings. Sensor drift within a day was negligible; moreover, differences between bottle samples and electrode measurements within a sampling day were smaller than differences across days. Bootstrap analysis indicated that conducting a daily in situ calibration would reduce the mean difference to 0.002 pH units and increase the number of samples within a 0.2 pH unit error to 98%.
This study demonstrates the long-term stability of salinity measurements from Argo floats equippe... more This study demonstrates the long-term stability of salinity measurements from Argo floats equipped with inductive conductivity cells, which have extended float lifetimes as compared to electrode-type cells. New Argo float sensor payloads must meet the demands of the Argo governance committees before they are implemented globally. Currently, the use of CTDs with inductive cells designed and manufactured by RBR, Ltd., has been approved as a Global Argo Pilot. One requirement for new sensors is to demonstrate stable measurements over the lifetime of a float. To demonstrate this, data from four Argo floats in the western Pacific Ocean equipped with the RBRargo CTD sensor package are analyzed using the same Owens–Wong–Cabanes (OWC) method and reference datasets as the Argo delayed-mode quality control (DMQC) operators. When run with default settings against the standard DMQC Argo and CTD databases, the OWC analysis reveals no drift in any of the four RBRargo datasets and, in one case, an...
Moderate resolution satellite imagery was combined with in-situ observations of suspended sedimen... more Moderate resolution satellite imagery was combined with in-situ observations of suspended sediment flux from the Sacramento-San Joaquin River Delta to gain an understanding of event-scale suspended sediment budgets for San Francisco Bay. The event-scale budgets estimated were dependent on tidal conditions, duration of the highflow event, and the timing of the remote observation during the high-flow event. The exported fraction of suspended material entering the Bay from the Delta during high-flow conditions was greatest during ebb tides. Short, storm-driven high-flow events exported a larger fraction of their suspended sediment load than did longer-duration high-flow events such as spring snowmelts. The dependence of the event-scale budgets on environmental and meteorological conditions, combined with the lack of site-specific algorithms for estimating suspended sediment concentrations from remote observations, rendered inconclusive our attempts to develop a 'rule-of-thumb' regarding the fraction of sediment influx from large storms that passes through the system. It is possible that sitespecific algorithms and an increased sample size (i.e., more remote observations) combined with in-situ observations of sediment fluxes through the Golden Gate would improve the ability of the methods presented here to develop such a 'rule-of-thumb.'
The pelagic ecosystem of the open part of the Black Sea was analyzed from the point of view of it... more The pelagic ecosystem of the open part of the Black Sea was analyzed from the point of view of its temporal changes on interannual and seasonal basis. The material was collected during interdisciplinary expeditions to the Black Sea, between 1978–1996. The observed interannual variability is discussed for all plankton groups except protozooplankton. During 1980–1993 a gradual decrease of mean air temperature in winter and an increase in phytoplankton biomass in summer were observed. The lowest and the highest phytoplankton biomasses corresponded to high and low temperatures in 1980 and 1992 respectively. The climatic quasi-periodic 20-years oscillations of winter air temperature determine the general intensity of Black Sea current system and, as a result, favorable conditions for growth of phytoplankton. The analysis of historical phytoplankton data corroborates this hypothesis. According to surface chlorophyll “a” satellite measurements the interannual variations were seen in winter and spring during the period from 1978 to 1986.
The data on taxonomic composition, abundance, and biomass of phytoplankton and chlorophyll a conc... more The data on taxonomic composition, abundance, and biomass of phytoplankton and chlorophyll a concentration in the eastern part of the Mediterranean Sea during late summer period are given in the paper. Different methods of measurements of the chlorophyll a concentration are compared. All the quantitative characteristics of phytoplankton manifest the oligotrophic level of water productivity during the period under study. The spatial distribution of the abundance and biomass of phytoplankton and chlorophyll a concentration are significantly influenced by the mesoscale eddies of typical size 10-50 miles. The quantitative characteristics of phytoplankton in the coastal zone were usually higher, as compared with the open sea regions. As for vertical distribution of micro- and nanophytoplankton, the maximum cell concentrations occurred within the upper homogenous layer and in the layer of pycnocline. The vertical profiles of phytoplankton and chlorophyll a were compared with the profiles of fluorescence; the maximum of fluorescence corresponded to the maximum of chlorophyll a concentration and seemed to result from high concentration of picophytoplankton. The maximum of fluorescence also manifested itself in the cases when the cell densities in the layers of maximum if micro- and nanophytoplankton exceeded 104 cells per liter.
The pelagic ecosystem of the open part of the Black Sea is analyzed from the point of view of its... more The pelagic ecosystem of the open part of the Black Sea is analyzed from the point of view of its sustainability. The peculiarities of plankton community in the temperate region result in regular seasonal oscillations of high range, the biomass values varying 5–10 times during the year. In the coastal regions of the Black Sea the values of primary production, chlorophyll concentration, phyto- and zooplankton biomasses change according to typical pattern of seasonal variations of temperate and subtropical areas: spring bloom of phytoplankton is followed by its decrease due to both depletion of nutrients and grazing by herbivorous zooplankton in summer. At the same time in the open regions the bloom of phytoplankton occurs during winter, because in the cyclonic gyres main pycnicline rises into euphotic zone (so-called “Black-Sea upwelling”). Besides regular seasonal variations, long term interannual variations also take place. The evident example of such kind of changes is the pattern of fluctuations of phytoplankton biomass, that oscillates inversely to average air temperature in winter. Another example is the development of newcomer ctenophore Mnemiopsis leidyi in late 1980s, resulting in sharp decrease of zooplankton biomass. During previous decade mass development of jelly-fish Aurelia aurita took place. Taxonomic composition of phyto- and zooplankton also changes in response to influence outside.
The remote sensing data obtained by Coastal Zone Color Scanner (CZCS) on the satellite “Nimbus-7”... more The remote sensing data obtained by Coastal Zone Color Scanner (CZCS) on the satellite “Nimbus-7” collected during the period from 1978 to 1986 were used to analyse the seasonal variation of surface plant pigments distribution in the Black Sea, presented here on maps for each climatological month. The pattern of seasonal variations is typical for subtropical regions rather than for the temperate ones. The range of the absolute value of plant pigment surface concentration measured by remote sensing does not differ greatly from the values measured by direct methods.
A series of infrared NOAA satellite images of the northwestern Black Sea (resolution 1 km) and co... more A series of infrared NOAA satellite images of the northwestern Black Sea (resolution 1 km) and corresponding maps of chlorophyll “a” (SeaWiFS data, resolution 9 km) are analyzed for the period 1 June-28 August 1998. A major objective was detection of the movement of three synoptic-scale anticyclonic eddies over the continental slope and the entrainment of photopigment-rich coastal waters by them. The study examines the effects of wind direction on the visibility of eddies in the chlorophyll field, and attempts to identify conditions favoring the transport of chlorophyll-rich shelf waters into the sea's abyssal basin.
The annual cycle of the plankton dynamics in the central Black Sea is studied by a one‐dimensiona... more The annual cycle of the plankton dynamics in the central Black Sea is studied by a one‐dimensional vertically resolved physical‐biological upper ocean model, coupled with the Mellor‐Yamada level 2.5 turbulence closure scheme. The biological model involves interactions between the inorganic nitrogen (nitrate, ammonium), phytoplankton and herbivorous zooplankton biomasses, and detritus. Given a knowledge of physical forcing, the model simulates main observed seasonal and vertical characteristic features, in particular, formation of the cold intermediate water mass and yearly evolution of the upper layer stratification, the annual cycle of production with the fall and the spring blooms, and the subsurface phytoplankton maximum layer in summer, as well as realistic patterns of particulate organic carbon and nitrogen. The computed seasonal cycles of the chlorophyll and primary production distributions over the euphotic layer compare reasonably well with the data. Initiation of the spring...
A wealth of historical coastal water pH data has been collected using potentiometric glass electr... more A wealth of historical coastal water pH data has been collected using potentiometric glass electrodes, but the accuracy and stability of these sensors is poorly understood. Here we compared pH measurements from five potentiometric sensors incorporated into profiling Sea-Bird instrument packages and compared them to spectrophotometric measurements on discrete bottle samples collected at two to three depths associated with each cast. Differences ranged from 20.509 to 10.479 with a mean difference of 20.055 pH units. Ninety-two percent of the measurements were within60.2 pH units, but 1% of the measurements had differences greater than 0.322. Sensor performance was affected by depth, but most of the difference was associated with calibration shortcomings. Sensor drift within a day was negligible; moreover, differences between bottle samples and electrode measurements within a sampling day were smaller than differences across days. Bootstrap analysis indicated that conducting a daily in situ calibration would reduce the mean difference to 0.002 pH units and increase the number of samples within a 0.2 pH unit error to 98%.
This study demonstrates the long-term stability of salinity measurements from Argo floats equippe... more This study demonstrates the long-term stability of salinity measurements from Argo floats equipped with inductive conductivity cells, which have extended float lifetimes as compared to electrode-type cells. New Argo float sensor payloads must meet the demands of the Argo governance committees before they are implemented globally. Currently, the use of CTDs with inductive cells designed and manufactured by RBR, Ltd., has been approved as a Global Argo Pilot. One requirement for new sensors is to demonstrate stable measurements over the lifetime of a float. To demonstrate this, data from four Argo floats in the western Pacific Ocean equipped with the RBRargo CTD sensor package are analyzed using the same Owens–Wong–Cabanes (OWC) method and reference datasets as the Argo delayed-mode quality control (DMQC) operators. When run with default settings against the standard DMQC Argo and CTD databases, the OWC analysis reveals no drift in any of the four RBRargo datasets and, in one case, an...
Uploads
Papers by Nikolay Nezlin