Anthropogenic carbon in the East Greenland Current

Sections of dissolved inorganic anthropogenic carbon () based on 2002 data in the East Greenland Current (EGC) are presented. The has been estimated using a model based on optimum multiparameter analysis with predefined source water types. Values of have been assigned to the source water types through age estimations based on the transit time distribution (TTD) technique. The validity of this approach is discussed and compared to other methods. The results indicated that the EGC had rather high levels of in the whole water column, and the anthropogenic signal of the different source areas were detected along the southward transit. We estimated an annual transport of with the Denmark Strait overflow (σ_θ > 27.8 kg m⁻³) of ∼0.036 ± 0.005 Gt C y⁻¹. The mean concentration in this density range was ∼30 μmol kg⁻¹. The main contribution was from Atlantic derived waters, the Polar Intermediate Water and the Greenland Sea Arctic Intermediate Water.     

Sources and distribution of fresh water in the East Greenland Current

Fresh water flowing from the Arctic Ocean via the East Greenland Current influences deep water formation in the Nordic Seas as well as the salinity of the surface and deep waters flowing from there. This fresh water has three sources: Pacific water (relatively fresh cf. Atlantic water), river runoff, and sea ice meltwater. To determine the relative amounts of the three sources of fresh water, in May 2002 we collected water samples across the East Greenland Current in sections from 81.5°N to the Irminger Sea south of Denmark Strait. We used nitrate-phosphate relationships to distinguish Pacific waters from Atlantic waters, salinity to obtain the sum of sea ice melt water and river runoff water, and total alkalinity to distinguish the latter. River runoff contributed the largest part of the total fresh water component, in some regions with some inventories exceeding 12 m. Pacific fresh water (Pacific source water S ∼ 32 cf. Atlantic source water S ∼ 34.9) typically provided about 1/3 of the river runoff contribution. Sea ice meltwater was very nearly non-existent in the surface waters of all sections, likely at least in part as a result of the samples being collected before the onset of the melt season. The fresh water from the Arctic Ocean was strongly confined to near the Greenland coast. We thus conjecture that the main source of fresh water from the Arctic Ocean most strongly impacting deep convection in the Nordic Seas would be sea ice as opposed to fresh water in the liquid phase, i.e., river runoff, Pacific fresh water, and sea ice meltwater.     

Water column structure and statistics of Denmark Strait Overflow Water cyclones

Data from seven moorings deployed across the East Greenland shelfbreak and slope 280 km downstream of Denmark Strait are used to investigate the characteristics and dynamics of Denmark Strait Overflow Water (DSOW) cyclones. On average, a cyclone passes the mooring array every other day near the 900 m isobath, dominating the variability of the boundary current system. There is considerable variation in both the frequency and location of the cyclones on the slope, but no apparent seasonality. Using the year-long data set from September 2007 to October 2008, we construct a composite DSOW cyclone that reveals the average scales of the features. The composite cyclone consists of a lens of dense overflow water on the bottom, up to 300 m thick, with cyclonic flow above the lens. The azimuthal flow is intensified in the middle and upper part of the water column and has the shape of a Gaussian eddy with a peak depth-mean speed of 0.22 m/s at a radius of 7.8 km. The lens is advected by the mean flow of 0.27 m/s and self propagates at 0.45 m/s, consistent with the topographic Rossby wave speed and the Nof speed. The total translation velocity along the East Greenland slope is 0.72 m/s. The self-propagation speed exceeds the cyclonic swirl speed, indicating that the azimuthal flow cannot kinematically trap fluid in the water column above the lens. This implies that the dense water anomaly and the cyclonic swirl velocity are dynamically linked, in line with previous theory. Satellite sea surface temperature (SST) data are investigated to study the surface expression of the cyclones. Disturbances to the SST field are found to propagate less quickly than the in situ DSOW cyclones, raising the possibility that the propagation of the SST signatures is not directly associated with the cyclones.     

Liquid freshwater transport and Polar Surface Water characteristics in the East Greenland Current during the AO-02 Oden expedition

Dynamical features of the East Greenland Current (EGC) are synthesized from a survey conducted by the Swedish icebreaker Oden during the International Arctic Ocean - 02 expedition (AO-02) in May 2002 with emphasis on the liquid freshwater transport and Polar Surface Water. The data include hydrography and lowered acoustic doppler current profiler (LADCP) velocities in eight transects along the EGC, from the Fram Strait in the north to the Denmark Strait in the south. The survey reveals a strong confinement of the low-salinity polar water in the EGC to the continental slope/shelf—a feature of relevance for the stability of the thermohaline circulation in the Arctic Mediterranean. The southward transport of liquid freshwater in the EGC was found to vary considerably between the sections, ranging between 0.01 and 0.1 Sverdrup. Computations based on geostrophic as well as LADCP velocities give a section-averaged southward freshwater transport of 0.06 Sverdrup in the EGC during May 2002. Furthermore, Oden data suggest that the liquid freshwater transport was as large north of the Fram Strait as it was south of the Denmark Strait.     

The outflow from Hudson Strait and its contribution to the Labrador Current

This study describes the first year round observations of the outflow from Hudson Strait as obtained from a moored array deployed mid-strait from August 2004–2005, and from a high-resolution hydrographic section conducted in September 2005. The outflow has the structure of a buoyant boundary current spread across the sloping topography of its southern edge. The variability in the flow is dominated by the extreme semi-diurnal tides and by vigorous, mostly barotropic, fluctuations over several days. The fresh water export is seasonally concentrated between June and March with a peak in November–December, consistent with the seasonal riverine input and sea-ice melt. It is highly variable on weekly timescales because of synchronous salinity and velocity variations. The estimated volume and liquid fresh water transports during 2004–2005 are, respectively, of 1–1.2 Sv and 78–88 (28–29) mSv relative to a salinity of 34.8 (33). This implies that the Hudson Strait outflow accounts for approximately 15% of the volume and 50% of the fresh water transports of the Labrador Current. This larger than previously estimated contribution is partially due to the recycling, within the Hudson Bay System, of relatively fresh waters that flow into Hudson Strait, along its northern edge. It is speculated that the source of this inflow is the outflow from Davis Strait.     

The East Greenland Spill Jet as an important component of the Atlantic Meridional Overturning Circulation

The recently discovered East Greenland Spill Jet is a bottom-intensified current on the upper continental slope south of Denmark Strait, transporting intermediate density water equatorward. Until now the Spill Jet has only been observed with limited summertime measurements from ships. Here we present the first year-round mooring observations demonstrating that the current is a ubiquitous feature with a volume transport similar to the well-known plume of Denmark Strait overflow water farther downslope. Using reverse particle tracking in a high-resolution numerical model, we investigate the upstream sources feeding the Spill Jet. Three main pathways are identified: particles flowing directly into the Spill Jet from the Denmark Strait sill; particles progressing southward on the East Greenland shelf that subsequently spill over the shelfbreak into the current; and ambient water from the Irminger Sea that gets entrained into the flow. The two Spill Jet pathways emanating from Denmark Strait are newly resolved, and long-term hydrographic data from the strait verifies that dense water is present far onto the Greenland shelf. Additional measurements near the southern tip of Greenland suggest that the Spill Jet ultimately merges with the deep portion of the shelfbreak current, originally thought to be a lateral circulation associated with the sub-polar gyre. Our study thus reveals a previously unrecognized significant component of the Atlantic Meridional Overturning Circulation that needs to be considered to understand fully the ocean׳s role in climate.     

The East Greenland Coastal Current: Structure, variability, and forcing

The subtidal circulation of the southeast Greenland shelf is described using a set of high-resolution hydrographic and velocity transects occupied in summer 2004. The main feature is the East Greenland Coastal Current (EGCC), a low-salinity, high-velocity jet with a wedge-shaped hydrographic structure characteristic of other surface buoyancy-driven currents. The EGCC was observed along the entire Greenland shelf south of Denmark Strait, while the transect north of the strait showed only a weak shelf flow. This observation, in conjunction with water mass considerations and other supporting evidence, suggests that the EGCC is an inner branch of the East Greenland Current (EGC) that forms south of Denmark Strait. It is argued that bathymetric steering is the most likely reason why the EGC apparently bifurcates at this location. Repeat sections occupied at Cape Farewell between 1997 and 2004 show that the alongshelf wind stress can have an influence on the structure and strength of the EGCC and EGC on timescales of 2-3 days. Accounting for the wind-induced effects, the volume transport of the combined EGCC/EGC system is roughly constant (∼2 Sv) over the study domain, from 68°N to Cape Farewell near 60°N. The corresponding freshwater transport increases by roughly 60% over this distance (59-96 mSv, referenced to a salinity of 34.8). This trend is consistent with a simple freshwater budget of the EGCC/EGC system that accounts for meltwater runoff, melting sea-ice and icebergs, and net precipitation minus evaporation.     

Transports of Nordic Seas water masses and excess SF6 through Fram Strait to the Arctic Ocean

To determine the exchanges between the Nordic Seas and the Arctic Ocean through Fram Strait is one of the most important aspects, and one of the major challenges, in describing the circulation in the Arctic Mediterranean Sea. Especially the northward transport of Arctic Intermediate Water (AIW) from the Nordic Seas into the Arctic Ocean is little known. In the two-ship study of the circulation in the Nordic Seas, Arctic Ocean - 2002, the Swedish icebreaker Oden operated in the ice-covered areas in and north of Fram Strait and in the western margins of Greenland and Iceland seas, while RV Knorr of Woods Hole worked in the ice free part of the Nordic Seas. Here two hydrographic sections obtained by Oden, augmented by tracer and velocity measurements with Lowered Acoustic Doppler Current Profiler (LADCP), are examined. The first section, reaching from the Svalbard shelf across the Yermak Plateau, covers the region north of Svalbard where inflow to the Arctic Ocean takes place. The second, western, section spans the outflow area extending from west of the Yermak Plateau onto the Greenland shelf. Geostrophic and LADCP derived velocities are both used to estimate the exchanges of water masses between the Nordic Seas and the Arctic Ocean. The geostrophic computations indicate a total flow of 3.6 Sv entering the Arctic on the eastern section. The southward flow on the western section is found to be 5.1 Sv. The total inflow to the Arctic Ocean obtained using the LADCP derived velocities is much larger, 13.6 Sv, and the southward transport on the western section is 13.7 Sv, equal to the northward transport north of Svalbard. Sulphur hexafluoride (SF₆) originating from a tracer release experiment in the Greenland Sea in 1996 has become a marker for the circulation of AIW. From the geostrophic velocities we obtain 0.5 Sv and from the LADCP derived velocities 2.8 Sv of AIW flowing into the Arctic. The annual transport of SF₆ into the Arctic Ocean derived from geostrophy is 5 kg/year, which is of the same magnitude as the observed total annual transport into the North Atlantic, while the LADCP measurements (19 kg/year) imply that it is substantially larger. Little SF₆ was found on the western section, confirming the dominance of the Arctic Ocean water masses and indicating that the major recirculation in Fram Strait takes place farther to the south.     

Evolution of the Kuroshio Tropical Water from the Luzon Strait to the east of Taiwan

This study examines the evolution of the Kuroshio Tropical Water (KTW) from the Luzon Strait to the I-Lan Ridge northeast of Taiwan. Historical conductivity temperature depth (CTD) profiles are analyzed using a method based on the calculation of the root mean square (rms) difference of the salinity along isopycnals. In combination with analysis of the distribution of the salinity maximum, this method enables water masses in the Kuroshio and the vicinity, to be tracked and distinguished as well as the detection of the areas where water masses are modified. Vertical and horizontal eddy diffusivities are then calculated from hydrographic and current velocity data to elucidate the dynamics underlying the KTW interactions with the surrounding water masses. Changes in KTW properties mainly occur in the southern half of the Luzon Strait, while moderate variations are observed east of Taiwan on the right flank of the Kuroshio. In spite of a front dividing the KTW from the South China Sea Tropical Water (SCSTW) on Kuroshio׳s western side, mixing between these two water masses seemingly occurs in the Luzon Strait. These water masses׳ interaction is not evident east of Taiwan. The estimation of eddy diffusivities yields high horizontal diffusivities (K_h~10² m² s⁻¹) all along the Kuroshio path, due to the high current shear along the Kuroshio׳s flanks. The vertical diffusivity approaches 10⁻³ m² s⁻¹, with the highest values in the southern Luzon Strait. Instabilities generated when the Kuroshio encounters the rough topography of this region may enhance both vertical and horizontal diffusivities there.     

丹麦海峡海洋锋时空变化特征研究

丹麦海峡海洋锋可为局地气候变化、海峡鱼类分布以及海峡中尺度涡等方面研究提供参考,在军事领域也具有较高应用价值。然而目前国内外缺乏对于丹麦海峡锋的系统研究。本文利用WOA13数据,对丹麦海峡锋位置、强度空间分布以及相应的季节变化进行了分析。结果显示,锋轴线位置在34°W以西150 m以浅相对稳定,34°W以东锋轴线随深度和季节均有摆动。锋强度在水平和垂直方向分布不均匀,水平方向上锋轴线最大值与最小值差值一般在3倍以上。垂直方向盐度锋主要集中在100 m以浅,且强度随深度不断减小;温度锋强度最大值在表层以下且在300 m以深随深度增加锋强度减小,但有一些区域如27°W和28°W附近,受到海底地形的影响温度锋强度随着深度的变化有大幅度增加的特点。     

Spatial and temporal variability of the North Korean Cold Water leading to the near-bottom cold water intrusion in Korea Strait

In the deepest region of Korea Strait, the surface temperature is highest in August (lowest in March), while the near-bottom temperature is lowest in September (highest in May). Cross-spectral analysis of the monthly temperature data between the two layers shows high coherence at the annual frequency with phase of 154°. Why and how does such a nearly opposite phasing occur between the surface and the near-bottom temperatures there? This study aims at answering these questions using historical and recently observed data.Cold and relatively fresh subsurface water flowing southward along the east coast of Korea and, known as the North Korean Cold Water (NKCW), becomes noticeable in April near the Sokcho coast. The zonal temperature gradient there is largest around June. The width of the NKCW becomes larger from April to August. After October, the NKCW retreats back toward the coast. The southward movement of the NKCW is thus strong over a period of six to seven months and weak in winter, especially in February. The NKCW flows southward relatively quickly along the coast in April to October and arrives at the Ulleung Basin within one to two months. Because of the sill between the Ulleung Basin and Korea Strait, this water cannot continue to flow to south, but piles up for about two to three months before it moves over the sill. The convergence of the subsurface cold water in the Ulleung Basin displaces the isopycnals upward and this water then intrudes over the sill along the isopycnals. This explains why in April or May, when this water appears noticeably at the Sokcho coast, the near-bottom water in Korea Strait is warmest and in August or September when the NKCW, which is piled up enough at the southern end of the Ulleung Basin, intrudes to Korea Strait, the near-bottom temperatures there are at their lowest.The origin of the NKCW seems to be the water of salinity less han 34.1 psu and surface density of 27σ_θ or higher, which sinks in the northwestern East Sea in January-March. The sinking of the water results from surface cooling in winter and is intensified due to the strong negative windstress curl. The cold and relatively fresh water, formed in the northwestern East Sea, is hypothesized to flow to the Ulleung Basin along three major paths, along the east coast of Korea, through the channel north of Ulleung-do Island, and through the channel between Ulleung-do and Dok-do Islands.     

Interannual salinity variations in the Tsushima Strait and its relation to the Changjiang discharge

Interannual salinity variations in the Tsushima Strait are investigated on the basis of historical hydrographic data. The EOF analysis revealed that the most dominant mode is the in-phase salinity variation between the eastern and western channels. The time coefficients of the EOF first mode in summer show a negative correlation with the Changjiang discharge, which indicates that salinity in the Tsushima Strait tends to decrease over summer, related to a large discharge of the Changjiang. The eigenvectors of the first mode are larger in the eastern channel than those in the western channel, though the low salinity water mainly flows through the western channel. This is because the low salinity water spreads into the eastern channel as well as the western channel over summers with a large discharge of the Changjiang. The out-of-phase salinity variation between the channels is extracted as the EOF second mode; this is the predominant variation in the western channel. The time coefficients of the second mode in summer show no significant correlations to the volume transports through the western channel and the transport differences between channels. A relationship between the EOF second mode and variations in the wind stress over the East China Sea is suggested.     

Transfer of lipids from plankton to blubber of harp and hooded seals off East Greenland

Sub-Arctic marine ecosystems are some of the most productive ecosystems in the world's oceans. The capacity of herbivorous zooplankton, such as Calanus, to biosynthesize and store large amounts of lipids during the short and intense spring bloom is a fundamental adaptation which facilitates the large production in these ecosystems. These energy-rich lipids are rapidly transferred through the food chain to Arctic seals. The fatty acids and stable isotopes from harp seal (Phoca groenlandica) and hooded seal (Cystophora cristata) off East Greenland as well as their potential prey, were analysed. The results were used to describe the lipid dynamics and energy transfer in parts of the East Greenland ecosystem. Even if the two seal species showed considerable overlap in diet and occurred at relatively similar trophic levels, the fatty acid profiles indicated that the bases of the food chains of harp and hooded seals were different. The fatty acids of harp seals originate from diatom-based food chain, whereas the fatty acids of hooded seals originate from dinoflagellate and the prymnesiophyte Phaeocystis pouchetii-based food chain. Stable isotope analyses showed that both species are true carnivores on the top of their food chains, with hooded seal being slightly higher on the food chain than harp seal.     

Monthly Variations of Water Masses in the Yellow and East China Seas, November 6, 1998

The monthly water mass variations in the Yellow Sea and the East China Sea are investigated using over 40 years of historical temperature and salinity observations via a cluster analysis that incorporates geographical distance and depth separation in addition to the temperature and salinity. Results delineate monthly variations in the major water masses and provide some insight into formation mechanisms and intermixing. The major water masses include the Kuroshio-East China Sea water (KE), the Yellow Sea surface water (YSS) and bottom cold water (YSB), mixed water (MW), and coastal water (CW). The distribution of the KE water mass reveals the intrusion pattern into the area west of Cheju. A separate mixed water type appears between the KE water mass and the Yellow Sea water masses during winter. The formation mechanism of the YSB appears to be the surface cooling and active mixing in winter. In the East China Sea, during summer, surface water is differentiated from the subsurface water while there is no differentiation during winter. In the Yellow Sea, a three layer system exists in the summer and fall (May–November) while a two layer system exists during the rest of the year. A fresh water mass generated by Yangtze River discharge (YD) is present over the northern East China Sea and the southern Yellow Sea during summer. This revised version was published online in August 2006 with corrections to the Cover Date.     

东海南部陆架水体2011年夏季温盐结构及其对台湾暖流和黑潮入侵的指示

利用2011年7月5个断面共30个站位的温盐深（CTD）测量资料,分析东海南部陆架水体的温盐结构和温跃层特征,探讨黑潮和台湾暖流对东海陆架水文状况的影响。结果显示,本区广泛存在着浅部温跃层和深部温跃层。浅部温跃层分布于20 m水深以内,跃层强度普遍较弱,具有明显的日内生消变化。深部温跃层分布于中、外陆架和台湾海峡。在中、外陆架的深水区,跃层底界深度约80 m,跃层厚度约10 m;跃层强度大,约为0.8 ℃/m,且较为稳定。在台湾海峡北部,温跃层分布于水深14～30 m,跃层厚度6～10 m,跃层强度偏弱,为0.2～0.5 ℃/m。在温跃层附近,由于上、下层水团温度、盐度的差异,其混合过程常出现盐指现象。在东海陆架90～110 m等深线之间,深部温跃层之下盘踞着一个深层冷水团,水温为16.8～17.6 ℃。黑潮水的入侵,使得外陆架温跃层强度减弱至0.2～0.5 ℃/m;同时,跃层层位上升,厚度加大。温跃层强度可以作为指示黑潮入侵的灵敏指标。当夏季深部温跃层强度低于0.6 ℃/m,同时伴随跃层厚度加大时,可判别为黑潮入侵。本区夏季黑潮锋可以到达110 m等深线附近。在中陆架50～80 m等深线之间,深部温跃层的消失,说明台湾暖流的强烈影响遍及整个水柱;而从南向北,台湾暖流的影响逐渐减弱。台湾海峡北部深层水温度较低,平均值为22.52 ℃,要比东海南部中陆架深层水低3 ℃,这可能意味着台湾暖流深层水主要源于黑潮分支的加入。     

夏季台湾海峡水及黑潮次表层涌升水向东海近陆架区营养盐输送通量的估算

According to historical mean ocean current data through the field observations of the Taiwan Ocean Research Institute during 1991–2005 and survey data of nutrients on the continental shelf of the East China Sea(ECS) in the summer of 2006, nutrient fluxes from the Taiwan Strait and Kuroshio subsurface waters are estimated using a grid interpolation method, which both are the sources of the Taiwan Warm Current. The nutrient fluxes of the two water masses are also compared. The results show that phosphate(PO4-P), silicate(SiO3-Si) and nitrate(NO3-N) fluxes to the ECS continental shelf from the Kuroshio upwelling water are slightly higher than those from the Taiwan Strait water in the summer of 2006. In contrast, owing to its lower velocity, the nutrient flux density(i.e., nutrient fluxes divided by the area of the specific section) of the Kuroshio subsurface water is lower than that of the Taiwan Strait water. In addition, the Taiwan Warm Current deep water, which is mainly constituted by the Kuroshio subsurface water, might directly reach the areas of high-frequency harmful alga blooms in the ECS.     

Mean flow and variability in the southwestern East Sea

The Ulleung Basin is one of three deep basins that are contained within the East/Japan Sea. Current meter moorings have been maintained in this basin beginning in 1996. The data from these moorings are used to investigate the mean circulation pattern, variability of deep flows, and volume transports of major water masses in the Ulleung Basin with supporting hydrographic data and help from a high-resolution numerical model. The bottom water within the Ulleung Basin, which must enter through a constricted passage from the north, is found to circulate cyclonically—a pattern that seems prevalent throughout the East Sea. A strong current of about 6 cms⁻¹ on average flows southward over the continental slope off the Korean coast underlying the northward East Korean Warm Current as part of the mean abyssal cyclonic circulation. Volume transports of the northward East Korean Warm Current, and southward flowing East Sea Intermediate Water and East Sea Proper Water are estimated to be 1.4 Sv (1 Sv=10⁻⁶ m³ s⁻¹), 0.8 Sv, and 3.0–4.0 Sv, respectively. Deep flow variability involves a wide range of time scales with no apparent seasonal variations, whereas the deep currents in the northern East Sea are known to be strongly seasonal.