Iron in the water column of the Weddell Sea

Total, dissolved and suspended iron has been determined in the water column of the Weddell Sea area during the austral summer 1988–1989. Some data are also presented for dissolved manganese, suspended manganese and suspended aluminium. The average value for dissolved iron was found to be 1.2 nM, with somewhat higher values at the Filchner Ice Shelf. The total iron was found to be considerably higher, with a range between 1 and 6 nM in the central Weddell Sea and 1 and 25 nM at the shelves. Transport of iron from the shelves into the Weddell Sea basin is demonstrated. This is observed both for total and dissolved iron.     

Subtropical coccolithophores in the Weddell Sea

Eleven subtropical coccolithophore species were identified in three samples taken in the austral autumn from the Weddell Sea, Antarctic, between 69°S and 70°S, just south of the Antarctic Slope Front. This is the first report of coccolithophores present at such southern latitudes. We provide three hypotheses for their occurrence in the Weddell Sea: (1) Coccolithophore species have wider temperature tolerances than previously believed. (2) Coccolithophores found in the Weddell Sea were part of a remnant community from the Agulhas Current. (3) Coccolithophores were transported by a N–S eddy crossing the Brazil–Malvinas confluence region and then subsequently transported to the east by warm water eddies of the Antarctic Circumpolar Current to the study location. Further temperature tolerance experiments with coccolithophores are recommended.     

Tritium profiles in the Weddell Sea

Tritium data were collected between 1985 and 1987 on several cruises of the German research icebreaker “Polarstern” to the Weddell Sea. Maximum tritium concentrations in the surface waters are of the order of 200 mTU. The minimum values observed in the Weddell Sea Deep Water at about 1000 m depth are about 15–40 mTU. The bottom waters show tritium concentrations of about 70–100 mTU in the central gyre, increasing to about 120 mTU in the northwestern corner of the Weddell Sea. The overflowing Ice Shelf Water observed on the continental slope west of the Filchner Depression has tritium concentrations close to those of the surface waters, indicating rapid renewal of this water mass. The data reflect the rapid renewal of the bottom waters in the northwestern corner of the Weddell Sea and the mixing of bottom water from this boundary current into the bottom waters of the central Weddell Gyre.     

Increase of carbon dioxide in the bottom water of the Weddell Sea, Antarctica

High precision total CO₂ (TCO₂) data are presented from the NW Weddell Sea obtained during two cruises which were 3 years apart. A TCO₂ increase from 1993 to 1996 was observed in the newly formed bottom water, whereas no TCO₂ increase was found in the surrounding water masses. Accompanying this TCO₂ increase in the bottom water was an oxygen decrease. Obviously, bottom water with variable characteristics is produced along the margins of the Weddell Sea. Examination of possible causes leads to the conclusion that the bottom water variability is largely due to varying amounts of Warm Deep Water intruding onto the shelves of the Weddell Sea, thus changing the shelf water end-member of bottom water formation. Analysis of the data, using the observed differences of oxygen to perform a correction, suggested that some part of the TCO₂ increase of the bottom water is due to the increased level of anthropogenic CO₂. The TCO₂ increase of the bottom water is commensurate to a tentative annual increase of about 1 μmol kg⁻¹ in the surface water source of this bottom water. This would agree fairly well with the increase of the partial pressure of CO₂ in the atmosphere.     

Parameterization of vertical mixing in the Weddell Sea

A series of vertical mixing schemes implemented in a circumpolar coupled ice–ocean model of the BRIOS family is validated against observations of hydrography and sea ice coverage in the Weddell Sea. Assessed parameterizations include the Richardson number-dependent Pacanowski–Philander scheme, the Mellor–Yamada turbulent closure scheme, the K-profile parameterization, a bulk mixed layer model and the ocean penetrative plume scheme (OPPS). Combinations of the Pacanowski–Philander parameterization or the OPPS with a simple diagnostic model depending on the Monin–Obukhov length yield particularly good results. In contrast, experiments using a constant diffusivity and the traditional convective adjustment cannot reproduce the observations. An underestimation of wind-driven mixing in summer leads to an accumulation of salt in the winter water layer, inducing deep convection in the central Weddell Sea and a homogenization of the water column. Large upward heat fluxes in these simulations lead to the formation of unrealistic, large polynyas in the central Weddell Sea after only a few years of integration. Furthermore, spurious open-ocean convection affects the basin-scale circulation and leads to a significant overestimation of meridional overturning rates. We conclude that an adequate parameterization of both wind-induced mixing and buoyancy-driven convection is crucial for realistic simulations of processes in seasonally ice-covered seas.     

Improved Seismic Stratigraphy of the Mesozoic Weddell Sea

We present a compilation of more than 45,000 km of multichannel seismic data acquired in the last three decades in the Weddell Sea. In accordance with recent tectonic models and available drillhole information, a consistent stratigraphic model for depositional units W1–W5 is set up. In conjunction with existing aeromagnetic data, a chronostratigraphic timetable is compiled and units W1.5, W2 and W3 are tentatively dated to have ages of between 136 Ma and 114 Ma. The age of W3 is not well constrained, but might be younger than 114 Ma. The data indicate that the thickest sediments are present in the western and southern Weddell Sea. These areas formed the earliest basins in the Weddell Sea and so the distribution of Mesozoic sediments is in accordance with the tectonic development of the ocean basin. In terms of Cenozoic glacial sediments, the largest depocenters are situated in front of the Filchner–Ronne Shelf, i.e. at the Crary Fan, with a thickness of up to 3 km.     

A note on crustal structure between Antarctic Peninsula and East Antarctic craton across the shelf of southern Weddell Sea

Analysis of gravity data based on the Airy isostasy, magnetic depth estimates and few seismic refraction data taken together indicates a thinning of the crust between the Antarctic Peninsula and the East Antarctic craton below the Filchner and Ronne ice shelves.     

An estimate of the vertical diffusivity of the deep water

A simple advection-diffusion model is applied to the deep water of the North Pacific Ocean. The physical mixing parameter, i.e., the ratio of vertical advection velocity (W) to vertical eddy diffusivity (D), is obtained from the vertical distribution of a conservative property such as salinity. The rate of decomposition of organic matter is estimated from the oxygen consumption rate which is obtained from dissolved oxygen content. The calcium carbonate flux in the deep water is obtained from alkalinity. Using these values and the vertical distribution of a radioisotope,¹⁴C or²²⁶Ra, the vertical eddy diffusivity and the upwelling velocity are found to be 1.2 cm²/sec and 1.4 ×10^–5 cm/sec, respectively, at the Geosecs 1969 station. The oxygen consumption rate at 3 km depth of the station is found to be 1.4×10^–3ml/l/yr.     

Particle flux through the Huanghai Sea cold water mass

Settling particulate matter （SPM） was collected by using sediment traps at four stations in a survey section from Qingdao to Cheju-do, across the Huanghai Sea cold water mass （HSCWM）, in August 2002. The sediment traps were planted in three layers： the upper layer of the thermocline （ULT） above the HSCWM, the lower layer of the thermocline （LLT）, and the bottom layer of water column （BL）. To determine the particle flux, the contents of organic carbon （POC）, organic nitrogen （PON）, total carbon （PC）, and total phosphorous （PP） in SPM were analyzed, and two flux models （Ⅰ and Ⅱ） were improved to calculate the resuspension ratio, with an assumption in Model Ⅰ that the vertical flux of SPM in the LLT equals the net vertical flux of SPM in the whole water column. An X value, i.e., the fraction of the resuspension flux originating from the surficial sediments nearby the sampling station, was deduced from Model Ⅰ to estimate the contribution of lateral currents to the total resuspension flux. The results showed that inorganic particles, fecal pellets, and miscellaneous aggregates were the major types of SPM in the HSCWM, and the contents of POC, PON, PC, and PP all decreased with water depth. A great deal of fecal pellets found in the LLT indicates that the main space producing biogenic SPM is the thermocline, and especially the LLT, where the C/N ratio is lower than that in the ULT. The resuspension ratios, 90%-96% among stations, imply strong impact ofresuspension on particle flux in the BL. These values were not significantly different between the two flux models, suggesting that the hypothesis in Model Ⅰ that the flux in the LLT equaling the net flux to the bottom is acceptable for shallow waters with stratification like the HSCWM. The POC export ratio from the HSCWM ranges from 35% to 68%. It benefits from the short sinking distance in shallow water. The upwelling in the HSCWM enhanced the POC flux through the water mass, and the lateral currents provides up to being greater than 50% ofresuspension flux in the BL according to evaluation of the X value.     

Mesoscale Variability of the Ocean in the Northern Part of the Weddell Sea

Oceanology - Results of a mesoscale survey in the Powell Basin in the northern part of the Weddell Sea are analyzed. The survey included 24 CTD casts (6 × 4) with an interval of six nautical...     

An estimate of fish biomass at the bottom layer of the Bohai Sea

The biomasses of fishes at the bottom layer of the Bohai Sea are extimated by analysing the data on samples (447 hauls,more than 0.2 million in number or 20 t in weight of fishes) collected monthly by our institute from April, 1982 to May, 1983 by a pair of bottom trawls through the Bohai Sea. The exploitation problems are also discussed in this paper.     

北黄海冷水团季节变化特征分析

基于2006至2007年“908”项目执行期间春夏秋冬共四个航次的CTD温盐数据,针对四个季节底层大面及大连一成山头断面温度和盐度的分布特征,分析了北黄海冷水团的季节变化,初步探讨了其消长过程,并与历史资料相比较,发现了关于北黄海冷水团的新问题。研究表明：夏季,北黄海冷水团温度和盐度与历史资料相比,低温中心位置存在东偏,但低温中心温度和盐度变化不大。春季,32．8psu高盐水舌主轴位置较冬季偏西约75km,123．5°E以东的原冬季盐度高值区的范围向北延伸的势力大减,退化为较弱的小高盐水舌冬。冬季,北黄海冷水团已经消失,黄海暖流呈舌状向北延伸。秋季,减弱的北黄海冷水团存在两个中心温度约9℃的低温中心。     

印尼贯穿流源区马鲁古海和哈马黑拉海水团来源的气候态分析

本文利用World Ocean Atlas 2013（WOA2013）气候态的温盐资料和the Simple Ocean Data Assimilation （SODA v3.3.1）流场数据,分析印尼贯穿流东部源区马鲁古海和哈马黑拉海的水团垂向分布特征及其来源,特别是次表层、中层及深层水的来源和路径。结果表明,气候态下,马鲁古海次表层的高温高盐水来自于北太平洋,与北太平洋热带水性质接近,哈马黑拉海次表层主要是来自南太平洋热带水;中层水以低温低盐为特征,马鲁古海的中层水来自南太平洋,受南极中层水控制,哈马黑拉海的中层水可能是从马鲁古海而来的南太平洋水;对于次表层和中层之间的过渡层,马鲁古海与哈马黑拉海的水源为南、北太平洋的混合水,且两个海域之间也存在着水团交换;在深层,马鲁古海的水源更倾向于班达海北部及塞兰海,而与太平洋水无关,哈马黑拉海由于地形阻挡也难以与太平洋直接发生水团交换。     

A geomorphological seabed classification for the Weddell Sea,Antarctica

Sea floor morphology plays an important role in many scientific disciplines such as ecology, hydrology and sedimentology since geomorphic features can act as physical controls for e.g. species distribution, oceanographically flow-path estimations or sedimentation processes. In this study, we provide a terrain analysis of the Weddell Sea based on the 500 m × 500 m resolution bathymetry data provided by the mapping project IBCSO. Seventeen seabed classes are recognized at the sea floor based on a fine and broad scale Benthic Positioning Index calculation highlighting the diversity of the glacially carved shelf. Beside the morphology, slope, aspect, terrain rugosity and hillshade were calculated and supplied to the data archive PANGAEA. Applying zonal statistics to the geomorphic features identified unambiguously the shelf edge of the Weddell Sea with a width of 45–70 km and a mean depth of about 1200 m ranging from 270 m to 4300 m. A complex morphology of troughs, flat ridges, pinnacles, steep slopes, seamounts, outcrops, and narrow ridges, structures with approx. 5–7 km width, build an approx. 40–70 km long swath along the shelf edge. The study shows where scarps and depressions control the connection between shelf and abyssal and where high and low declination within the scarps e.g. occur. For evaluation purpose, 428 grain size samples were added to the seabed class map. The mean values of mud, sand and gravel of those samples falling into a single seabed class was calculated, respectively, and assigned to a sediment texture class according to a common sediment classification scheme.     

安达曼海的热收支分析及其水交换研究

The characteristics of the T/S structures, water mass exchange and deep circulation in the Andaman Sea are investigated based on the simulation from a high-resolution general circulation model(MITgcm). The results show that, below 1 000 m, the water mass is saltier, warmer and more homogeneous in the Andaman Sea than that in the Bay of Bengal, attributing to the strong vertical mixing at the depth of ～1 800 m. The water mass exchange between the Andaman Sea and the Bay of Bengal goes through three major channels, which manifests itself as follows: the northern channel(Preparis Channel) is the main passage of water mass transport from the Bay of Bengal to the Andaman Sea, whereas the Middle Channel(the south of Andaman Islands and the north of Nicobar Islands) has an opposite transport; the southern channel(Great Channel) features with a four-layer water exchange which results in the least net transport among the three channels; all the transports through the three channels have an intra-annual variation with a period of half a year. At 1 000-m depth, the entire Andaman Sea is occupied by a cyclonic circulation in January and July while by an anticyclonic one in April and October. The semiannual cycle found in both the deep circulation and water mass exchange is likely associated with the downwelling eastward-propagating Kelvin waves induced by the semiannual westerly component in the equatorial Indian Ocean during intermonsoon seasons.     

南极西北威德尔海上层海洋湍流混合研究

Turbulent mixing in the upper ocean(30-200 m) of the northwestern Weddell Sea is investigated based on profiles of temperature,salinity and microstructure data obtained during February 2014.Vertical thermohaline structures are distinct due to geographic features and sea ice distribution,resulting in that turbulent dissipation rates(ε) and turbulent diffusivity(K) are vertically and spatially non-uniform.On the shelf north of Antarctic Peninsula and Philip Ridge,with a relatively homogeneous vertical structure of temperature and salinity through the entire water column in the upper 200 m,both ε and K show significantly enhanced values in the order of O(10~(-7))-O(10~(-6)) W/kg and O(10~(-3))-O(10~(-2)) m~2/s respectively,about two or three orders of magnitude higher than those in the open ocean.Mixing intensities tend to be mild due to strong stratification in the Powell Basin and South Orkney Plateau,where s decreases with depth from O(10~(-8)) to O(10~(-9)) W/kg,while K changes vertically in an inverse direction relative to s from O(10~(-6)) to O(10~(-5)) m~2/s.In the marginal ice zone,K is vertically stable with the order of10~(-4) m~2/s although both intense dissipation and strong stratification occur at depth of 50-100 m below a cold freshened mixed layer.Though previous studies indentify wind work and tides as the primary energy sources for turbulent mixing in coastal regions,our results indicate weak relationship between K and wind stress or tidal kinetic energy.Instead,intensified mixing occurs with large bottom roughness,demonstrating that only when internal waves generated by wind and tide impinge on steep topography can the energy dissipate to support mixing.In addition,geostrophic current flowing out of the Weddell Sea through the gap west of Philip Passage is another energy source contributing to the local intense mixing.