Igor M. Belkin

Temporal variation in the sediment load of the Yangtze river and the influences of human activities

Data on sediment discharge and suspended sediment concentration (SSC) at two hydrological stations from 1951 to 2000 were utilized to study the variation in river sediment supply to the delta. Literature and documents on dam construction and water withdrawal were collected, and combined with field investigations on deforestation/afforestation and extraction of riverbed sediment, to examine the influence of human activities on river sediment load. From 1950s to 1960s, the river sediment discharge and SSC increased by 10 and 12%, respectively. Since 1960s, both values have shown a significant reduction, with sediment discharge 34% lower and SSC 38% lower in the 1990s than in the 1960s. These changes are found to be governed by the balance between two aspects of human activities: deforestation and dam construction. It was predicted that river sediment discharge and SSC in the future 100 years would probably be reduced to less than 50% of the present (the average of the past 50 years) due to human activities especially the Three Gorges Dam, which will be put into operation in 2003. The effect of this reduction on the deltaic coast is also briefly addressed.

Climatology and seasonal variability of ocean fronts in the East China, Yellow and Bohai seas from satellite SST data

Front detection and declouding algorithms developed at the URI have been applied to the 12-year (1985–1996) Pathfinder SST data set to produce the first comprehensive, objectively derived, year-round climatology of ocean thermal fronts in the eastern China Seas, from 24°N to 41°N. Ten fronts have been distinguished, namely Kuroshio, Zhejiang-Fujian, Jiangsu, Shandong Peninsula, Bohai Sea, Seohan Bay, Kyunggi Bay, Western and Eastern Chejudo (South Korean Coastal Front), and Yangtze Bank Ring Front. The fronts are seasonally persistent: they emerge and disappear in the same seasons of different years. The frontal pattern remains fairly stable from one year to another, whereas individual fronts display different modes of seasonal variability.

Accelerated Warming and Emergent Trends in Fisheries Biomass Yields of the World's Large Marine Ecosystems

Abstract Information on the effects of global climate change on trends in global fisheries biomass yields has been limited in spatial and temporal scale. Results are presented of a global study of the impact of sea surface temperature (SST) changes over the last 25 years on the fisheries yields of 63 large marine ecosystems (LMEs) that annually produce 80% of the worlds marine fisheries catches. Warming trends were observed in 61 LMEs around the globe. In 18 of the LMEs, rates of SST warming were two to four times faster during the past 25 years than the globally averaged rates of SST warming reported by the Intergovernmental Panel on Climate Change in 2007. Effects of warming on fisheries biomass yields were greatest in the fast-warming northern Northeast Atlantic LMEs, where increasing trends in fisheries biomass yields were related to zooplankton biomass increases. In contrast, fisheries biomass yields of LMEs in the fast-warming, more southerly reaches of the Northeast Atlantic were declining in response to decreases in zooplankton abundance. The LMEs around the margins of the Indian Ocean, where SSTs were among the worlds slowest warming, revealed a consistent pattern of fisheries biomass increases during the past 25 years, driven principally by human need for food security from fisheries resources. As a precautionary approach toward more sustainable fisheries utilization, management measures to limit the total allowable catch through a cap-and-sustain approach are suggested for the developing nations recently fishing heavily on resources of the Agulhas Current, Somali Current, Arabian Sea, and Bay of Bengal LMEs.

East Hainan upwelling fronts detected by remote sensing and modelled in summer

Using the Belkin and O’Reilly algorithm and high-resolution (1 km) satellite sea surface temperature (SST) and chlorophyll-a (chl-a) data from 2002 to 2011, fronts were detected off the east/northeast coast of Hainan Island, South China Sea. These fronts were mainly produced by upwelling off eastern Hainan Island, through which cold, high-salinity, high-density, and nutrient-rich bottom water was brought to the surface and subsurface and then transported to the northeast of Hainan Island by the along-shore currents. The fronts are anisotropic, with a dominant orientation SSW–NNE. A three-dimensional ocean model forced by the Quick Scatterometer (QuikSCAT) winds was employed to study the three-dimensional structure of these fronts as well as the relationship between the fronts and upwelling or summer monsoon. The results show that the front intensity (cross-frontal gradient) is strongly correlated with the along-shore local winds, and has a strong seasonal and a weak inter-annual variation with a maximum of about 0.5°C km–1 at the subsurface (about 15 m) rather than the surface.

Russian Drifting Stations on Arctic Ice Islands

A summary of Russian discoveries of Arctic ice islands – peculiar tabular icebergs – is presented, complete with a chronological account of drifting stations installed on ice islands. Of 40 ‘North Pole’ drifting stations established from 1937 through 2013, six were set up on five ice islands: North Pole-6, 18/19 (same ice island), 22, 23, and 24. These ice islands served as reliable long-term research platforms as evidenced by the extensive bibliography of scientific publications based on observations made from manned ice island stations. Studies were conducted of structure and morphology of ice islands; under-ice biota; deep Arctic Ocean benthos; meteorology and climate; and oceanography. Biological collections from these ice islands are still being analyzed.

Thermal fronts of the southern South China Sea from satellite and in situ data

The major goal of this study was to find match-ups between thermal fronts mapped from satellite sea surface temperature (SST) imagery and from in situ data in the southern South China Sea (SSCS), using 11 ship surveys conducted by the South China Sea Institute of Oceanology (SCSIO) between 1987 and 1999. Fronts were automatically detected by the Cayula–Cornillon multi-image edge detection algorithm (CCA) applied to satellite-derived maps of the Advanced Very High Resolution Radiometer (AVHRR) SST obtained from the Pathfinder project (8364 twice-daily global fields with 9 km resolution between 1985 and 1996). Twice-daily near-instant frontal maps were composited without any averaging or smoothing to produce individual monthly frontal maps covering the period from January 1985 through December 1996 (144 maps in total). Although the SSCS is a tropical sea with little SST difference between water masses, the CCA turned out to be an effective tool for front mapping in the SSCS. Out of the 11 ship surveys analysed in this study, four surveys produced satisfactory match-ups. The percentage of match-ups is considered reasonably high given that (1) ship surveys were not optimized to cross fronts, therefore most in situ sections missed fronts; (2) satellite measurements of SST with AVHRR are hampered by cloudiness, therefore satellite-derived frontal maps might miss some fronts masked by persistent cloudiness. Fronts are more distinct in winter, when cross-frontal SST gradients are enhanced. From oceanographic vertical sections and horizontal maps, fronts are much sharper in the subsurface layer (represented here by 50 m level). Nonetheless, the CCA successfully detected SST fronts with a cross-frontal step as small as 1°C.

A peculiar lens-shaped structure observed in the South China Sea

Lens-shaped structures within thermocline potentially play a significant role in subsurface transport of mass, heat, and salt in the global ocean. Whilst such structures have been documented in many oceanic regions, none has been observed in the China Seas. This study reports on observations of a lens-shaped structure within thermocline in the southwestern South China Sea in September 2007. This structure had a maximum thickness of approximately 60 m and a horizontal extent exceeding 220 km. This lens was peculiar in that its size is larger than most similar structures documented in the literature. The lens core was characterized by well-mixed water with higher temperature (~28.8 °C), lower salinity (~33.3) and lower potential vorticity (PV) compared to the surrounding waters. Based on an ocean reanalysis, possible generation mechanism of the lens is explored by examining the evolution of surface and subsurface thermohaline properties, and an analysis of vertical PV flux. The lens was likely generated by a mixture of the local mixed-layer water and the water from the coastal jet separation site.