Amur Bay: Hydrological, Hydrochemical, and Microbiological Characteristics during Summer Monsoon

Abstract. Sri Lanka occupies a unique location within the equatorial belt in the northern Indian Ocean, with the Arabian Sea on its western side and the Bay of Bengal on its eastern side, and experiences bi-annually reversing monsoon winds. Aggregations of blue whale (Balaenoptera musculus) have been observed along the southern coast of Sri Lanka during the northeast (NE) monsoon, when satellite imagery indicates lower productivity in the surface waters. This study explored elements of the dynamics of the surface circulation and coastal upwelling in the waters around Sri Lanka using satellite imagery and numerical simulations using the Regional Ocean Modelling System (ROMS). The model was run for 3 years to examine the seasonal and shorter-term (~10 days) variability. The results reproduced correctly the reversing current system, between the Equator and Sri Lanka, in response to the changing wind field: the eastward flowing Southwest Monsoon Current (SMC) during the southwest (SW) monsoon transporting 11.5 Sv (mean over 2010–2012) and the westward flowing Northeast Monsoon Current (NMC) transporting 9.6 Sv during the NE monsoon, respectively. A recirculation feature located to the east of Sri Lanka during the SW monsoon, the Sri Lanka Dome, is shown to result from the interaction between the SMC and the island of Sri Lanka. Along the eastern and western coasts, during both monsoon periods, flow is southward converging along the southern coast. During the SW monsoon, the island deflects the eastward flowing SMC southward, whilst along the eastern coast, the southward flow results from the Sri Lanka Dome recirculation. The major upwelling region, during both monsoon periods, is located along the southern coast, resulting from southward flow converging along the southern coast and subsequent divergence associated with the offshore transport of water. Higher surface chlorophyll concentrations were observed during the SW monsoon. The location of the flow convergence and hence the upwelling centre was dependent on the relative strengths of wind-driven flow along the eastern and western coasts: during the SW (NE) monsoon, the flow along the western (eastern) coast was stronger, migrating the upwelling centre to the east (west).

ABSTRACTSeasonality of peak rainfall finds its application in several water resource activities such as deciding the timing of agriculture, regulation of water control structure, predicting the timing of floods; and understanding the lag between rainfall and floods. In a country like India, rainfall (which is the primary source of water) is influenced by different monsoon patterns, causing a disparity in its seasonality, thus, understanding the timing of the peak rainfall and its changes becomes crucial for water resources management. Here, the circular statistical approach is employed to understand the characteristics of peak rainfall (PRF) seasonality in India. It is observed that the western coast and central parts are influenced by the southwest monsoon (June–September) yielding strong seasonality. While, dominance of the northeast monsoon (October–December) is observed along the eastern coast with moderate to strong seasonality moving from north to south. The region lying between the west and the east coast is influenced by both southwest and northeast monsoons yielding bimodal seasonality of PRF. Also, northeast India is found to be influenced by both monsoon patterns. A weak seasonality of PRF is observed in the northern parts that are influenced by several factors like southwest monsoon, northeast monsoon, and snowfall (December–April). Three existing tests along with the proposed modified versions of Pettitt and Mann–Kendall tests are applied to detect changes in the seasonality of PRF. Grids identified with changes at 5% and 10% significance levels considering these tests showed significant differences in mean date and resultant length, and gradual shift in the dates of PRF. The analysis demonstrates the necessity of distinct water resource planning for different Indian regions. Also, changes in the timings of PRF implicate the effect of climate change, which demonstrates the need for a revision in water resources planning and management.

Grain size determinations were carried out for 54 beach-sand samples from the western (n = 25) and eastern (n = 29) coasts of the Gulf of California, Mexico, in order to establish the relationship among coastal processes, relief, and grain size parameters for both areas based on grain size distributions. This was done because both coastal areas are controlled by marine processes and the geomorphology of the coast, since fluvial discharges are negligible in the distribution of sands. In general, sands from the western coast are mainly coarse, moderately sorted, near-symmetrical with leptokurtic and very leptokurtic distributions. Correlations between grain-size parameters for the western coast are controlled by less selectivity in the coastal processes to concentrate fractions in a specific range of sizes, a narrow coastal plain, and compositional differences in the sands due to the heterogeneous lithology and the presence of carbonate shells. Eastern coast beach sands are medium, moderately well sorted, near-symmetrical with mesokurtic to leptokurtic distributions. Correlations between grain size parameters for the eastern coast are controlled by longshore current drifts in a northwestern direction and a wider coastal plain compared to the western coast.

We used the ocean general circulation model (OGCM) developed in the Massachusetts Institute of Technology to study the response of the Indo‐Pacific warm pool (IPWP) to net atmospheric freshwater flux (NAFW, equal to evaporation minus precipitation) at interannual timescales. The OGCM is forced by observed, monthly NAFW from 1988 to 2000. Our simulations show that the magnitude of interannual anomalies of salinity and temperature reaches about 0.7 practical salinity unit and 0.4°C, respectively. The typical timescale of these interannual variabilities is about 3–5 years. Averaged over 1988–2000, a decrease (increase) of temperature is accompanied with a decrease (increase) of salinity in the western Pacific and South Indian Ocean. A decrease of temperature, however, is accompanied with an increase of salinity in the surface layer (0–50 m) of the North Indian Ocean. The diagnosed budgets of salinity and temperature (heat) are analyzed to estimate the role of advection and vertical mixing in response to the surface NAFW forcing. The analyses indicate that the salinity anomaly in the IPWP is largely due to vertical mixing, especially in the surface layer. The vertical mixing of salinity, in turn, is associated with the surface NAFW anomaly. In contrast, the temperature anomaly above 300 m is primarily due to changes in advection forced by the NAFW, which is associated with basin‐wide changes in major ocean currents. Because of the strong effect of advection on the interannual variability of temperature, the temperature anomaly in the surface layer lags the salinity anomaly about 14–15 months. The results of our simulations are consistent with previous studies about the nearly immediate response of the tropical upper ocean to NAFW forcing due to vertical mixing. The slower response due to changes in basin‐scale heat advection suggests the possibility that ocean variability at interannual and longer timescales can be generated by large‐scale NAFW forcing at seasonal and longer timescales.

Although plankton bloom incidents in the upper Gulf of Thailand (UGoT) have been reported, no dynamic investigation of the phenomenon has been conducted. To address this need, a simple pelagic ecosystem model coupled with the Princeton Ocean Model (POM) was employed to investigate seasonal variations in surface chlorophyll-a (chl-a) distributions to clarify phytoplankton dynamics in this area. The results revealed patterns of seasonal chl-a distribution that correspond to local wind, water movement and river discharge. High chl-a patchiness was found to be concentrated near the western coast following westward circulation near the northern coast developed during the northeast monsoon. During the southwest monsoon high concentrations were observed around the northeastern coast due to eastward flow. The simulated results could explain the seasonal shifting of phytoplankton blooms, which typically arise along the western and eastern coasts during the northeast and the southwest monsoons, respectively. Sensitivity analyses of simulated chl-a distributions demonstrate that water stability, including wind-induced vertical currents and mixing, plays significant roles in controlling phytoplankton growth. Nutrients in the water column will not stimulate strong plankton blooms unless upwelling develops or vertical diffusivity is low. This finding suggests an alternative aspect of the mechanism of phytoplankton bloom in this region.

Results of long-term studies of zooplankton species in the Amur Bay (Japan Sea) are analyzed. Two seasonal «waves» of the allochtonous species are defined: the first in the early summer that is formed mainly by inter-zonal copepods spawning in the deep layers ( Metridia pacifica , Neocalanus plumchrus, Calanus glacialis ) and the second in the late summer that is represented by warm-water copepods of subtropical origin ( Calanus pacificus and Paracalanus parvus ) obviously transported from the southern Japan Sea by currents. The latter species is able to dominate in the zooplankton community of coastal waters in the early-autumn season. Variations of this mass species abundance in the Amur Bay under changes of wind-driven upwelling/downwelling circulation are investigated using an empirical advective model of its cross-shelf transport. There is found that strong summer southern on-shore winds (summer monsoon) are favourable for its high abundance but in these conditions it is transported toward the coast by the deep compensatory flow developed only after the summer monsoon change to the winter monsoon with opposite direction; that’s why the high abundance is observed in autumn, in September-October. In the years with weak summer monsoon the species is transported to the bay in mass by the surface on-shore wind-driven flow earlier, in August, but its number decreases after the monsoon change, so the maximum of abundance is not high. Patterns of the transport by cross-shelf currents depend supposedly on the depth of plankton concentration. Recent strengthening of summer monsoon causes heightening of P. parvus abundance in the coastal waters at southern Primorye, up to extreme high values in 2013, but climatic trend of the summer monsoon intensity is negative, so decreasing of this species transport toward Primorye coast and its abundance in the coastal waters, as the Amur Bay, can be expected in the nearest future.

An integrated novel approach to the environmental health assessment of Bangladesh's coastal ecosystems

Otolith shape and elemental composition: Complementary tools for stock discrimination of mulloway ( Argyrosomus japonicus) in southern Australia

A study on seasonal characteristics of phytoplankton dynamics and environmental factors was carried out at four stations including Mara-do and U-do located in the western and eastern coast of Jeju Island in southern Korea from April 2003 to March 2004. Out of 101 phytoplankton species identified, 84 belong to Bacillariophyceae, 9 Dinophyceae, 6 phytoflagellates and 2 coccolithophorids, and the highest value of species diversity was observed in April. Phytoplankton was more abundant at the western coast than at the eastern coast from March to September and its highest abundance was 49.24 10 cells L at Mara-do in July. The pennate diatoms were more abundant at the western coast than at the eastern coast with the highest abundance of 38.75 10 cells L at Mara-do in July, and during this period Nitzschia longissima contributed 68.5% of the total phytoplankton abundance. Naviculaceae was more abundant at Gosan (western coast) in November when Stauroneis membranacea represented 80.1% of the abundance. Leptocylindrus dances contributed 49.4% of the abundance at U-do in November. Dinophyceae was more abundant at U-do in August. Water temperature and pH fluctuated from 11.7 to 27.1 and from 7.31 to 8.70, respectively. Water temperature of Mara-do was about 1-2 higher than the other stations. Salinity varied from 30.4 to 35.0 psu with the minimum in rainy season and the maximum at the end of winter. The concentration of NH-N, NO-N, NO-N, PO-P and SiO-Si ranged 0.07-6.79, 1.0-62.0, 1.0-8.0, 1.0-7.0 and 7.0-191.0 g-at L, respectively. Chlorophyll a concentrations varied from 0.10 to 1.17 g L. NH-N concentrations were high at U-do from May to December, and at Mara-do from January to February. The high concentrations of NO-N were found at Mara-do from June to September and at U-do from January to May. The effects of various physicochemical parameters on the seasonal distribution and succession of phytoplankton population suggest that there is a classical pattern of phytoplankton dynamics in Jeju coastal waters.

The analysis of chlorophyll, sea surface temperature (SST), wind speed and nitrate data have been carried out in the monthly, seasonal and inter-annual scales during 1999–2004. The monthly averaged chlorophyll concentration indicates high chlorophyll concentration (0.50–2.0 mg/m3) in the southern peninsula around the tip of India. The movement of chlorophyll from the Arabian Sea and Gulf of Mannar region towards the east via Sri Lankan region has been observed during the southwest monsoon (SWM) season. The algal bloom has been observed both during southwest and northeast monsoon (NEM) period. The SST has been observed to be high (29–31 °C) during the spring inter monsoon (SIM) during March–May and low during SWM and NEM (~27 °C). Wind speed has been observed to be very high (8–12 m/s) during the SWM and NEM periods. The relationship between in situ nitrate and temperature has been established with R2 value 0.912 with 1537 data points. The nitrate concentration has been observed to be high (0.20–0.50 µmol/l) during SWM due to the upwelling process. Relationship has been established between chlorophyll, SST, wind speed and nitrate covering the seasonal averaged data over five-year period. The increase in wind speed may be causing upwelling and mixing phenomenon, bringing up the nutrient rich bottom water to surface and mixes up the water column and hence the decrease in SST. So, the enhancement in productivity/phytoplankton chlorophyll biomass has been observed. The interrelationship of the parameters in the Arabian Sea, Indian Ocean and the Bay of Bengal subsets has been derived. The chlorophyll in the Indian Ocean has been observed to be primarily dependent on nitrate (R2 = 0.39) and SST (R2 = 0.38) and to a lesser extent wind speed (R2 = 0.11). But, the Arabian Sea and Bay of Bengal chlorophyll has been observed to be more dependent on SST (R2 = 0.43 and 0.52) followed by nitrate (R2 = 0.30 and 0.27) and wind speed (R2 = 0.18 and 0.11), obtained from regression analysis.

Purpose. The paper is aimed at studying the hydrological regime of the Novik Bay (Russky Island, Peter the Great Bay, Sea of Japan). Methods and Results. Regular ship and ice cover CTD observations (more 1000 water column profiling stations) carried out in the Novik and Amur bays in 2013–2018 were used. Weather conditions in the region under study were analyzed based on the data of the Vladivostok weather station archive (WMO_ID=31960). Quantitative estimates of the drift and gradient currents in the bay are represented. Conclusions. Seasonal changes in the thermohaline stratification of the Peter the Great Bay coastal waters are conditioned by the monsoon climate features. The Novik Bay hydrological regime is additionally affected by its isolation and shallowness, as well as by the Russky Island relief. Weak water dynamics in the bay is observed during the summer monsoon (April – August) that is a result of the south winds blocking by the hills. The autumn-winter monsoon (when the north winds dominate) induces the water surge to the bay that, in its turn, blocks its circulation. The winter Siberian cold anticyclone forms the ice cover in the bay, and just in such an ice-forming season the salinity increase in the bottom layer is observed. In the shallow southern part of the Novik Bay, the process of ice formation begins. The downwelling flow of salty heavy water directed to the north out of the bay along the bottom relief is compensated by the counter flow of fresh waters from the Amur Bay which inflow to the upper sub-ice layer. The freeze-up period is most favorable for water renewal. The efficiency of this process is additionally influenced by a heat flow from bottom sediments and by the ice conditions in the adjacent water areas of the Peter the Great Bay

The nature and impact of relative sea level rise on the coastal areas of Bangladesh: trend analysis and vulnerability assessment

The glacial water properties and circulation changes in the North Pacific Ocean are investigated using a coupled ocean‐atmosphere‐sea‐ice climate model. With glacial boundary conditions, an increase in potential density in the upper layers of the northern North Pacific makes the water column highly unstable and eventually results in the enhancement of North Pacific Intermediate Water (NPIW) production, consistent with proxy evidence. The NPIW outflow reaches deeper layers than in the present‐day ocean, but remains largely confined to the North Pacific. The increase in potential density is predominantly caused by the increase in salinity and, to a lesser extent, by decreases in temperature. The increase in surface salinity is especially high in the Sea of Okhotsk and the western Bering Sea, which are possible source areas of glacial NPIW production. In these regions, an increase in brine release due to a marked increase in sea ice, evaporation exceeding precipitation, and a reduction in river discharge contribute to the increase in surface salinity. In short a reduction in freshwater input to the northern North Pacific is the main reason for the increase in the production and outflow of glacial NPIW.

Zooplankton in the deep-water zone of Lake Baikal features endemism, a specific trophic structure, intensive food relationships and pronounced interannual variability. In the late summer period, the dynamics of zooplankton at the deep-sea zone near the western (Point 1, village Bolshye Koty) and eastern (former BCBC area of wastewater discharge) coasts, taking into account natural conditions. The total number of zooplankton in the 0-100 m layer off the west coast was 2,493 thousand per/m2. Epischura baikalensis Sars 1900 prevails - more than 51 % (1260,76 thousand per/m2). The share of rotifers was 47 % (1138,0 thousand per/m2). The number of Cyclops kolensis Lilljeborg, 1901 was 13,7 thousand per/m2 and Bosmina longirostris Muller, 1785 - 15,98 thousand per/m2 which accounts for about 2 % of the total amount of zooplankton. The total number of zooplankton in the 0-100 m layer off the east coast was 2399,18 thousand per/m2. Epischura baikalensis dominates the zooplankton community - more than 57 % (1379,99 thousand per/m2). The share of rotifers was 40 % (965,1 thousand per/m2). The number of Cyclops kolensis was 49,62 thousand per/m2 and Bosmina longirostris - 4,51 thousand per/m2 which accounts for about 3% of the total amount of zooplankton. The average temperature values in the 0-100 m layer and water transparency at the western and eastern coasts differed slightly from the long-term average. At the western shore, the maximum surface concentration of chlorophyll «a» was 1,84 mg/m3 with an average value of 1,16± 0,27 mg/m3. At the eastern coast, the maximum concentration of chlorophyll «a» at a depth of 25 m was 2,41 mg/m3 with an average value of 1,39±0,31 mg/m3. No significant differences in the state of plankton were found at the western and eastern coasts of Southern Baikal.

The objective of this work was to detect and compare blood parameters of European flounder (Platichthys flesus), herring (Clupea harertgus membras), eelpout (Zoarces viviparous) and perch (Perca fluviatilis) at the Eastern and Western coast of the Gulf of Riga. The number of erythrocytes in herring of the Gulf of Riga ranges from 1.45 to 2.57 × 1012/L. At the same time no statistically significant difference in red blood cells (RBC) count between herring of both coasts was detected. The most common white blood cells in GoR herring blood smear were lymphocytes ranging from 73 to 94%. The number of lymphoblasts was very small (0–4%), indicating that herring of the GoR is not exposed to chronic stress. The number of erythrocytes in flounder ranged from 0.8 to 2.65 × 1012/L, but hemoglobin—from 4.7 to 16.5 g/dL. RBC count and hemoglobin level in European flounder did not differ between coasts however hematocrit was significantly higher at the Eastern coast. White blood cell count in flounder near the Western and Eastern coast was almost equal. Blood indices in eelpouts were slightly higher at the Eastern cost. Slightly higher number of red blood cells and significantly higher hemoglobin level has been observed in perch feeding near the Eastern coast, indicating physiological disturbances of fish. Although hematological analysis pointed at slightly worse living conditions of fish at the Eastern coast, in general hematological picture did not give evidence of fish welfare decline in the Gulf of Riga.