Holocene accumulation of organic carbon at the Laptev Sea continental margin (Arctic Ocean): sources, pathways, and sinks

Composition and accumulation rates of organic carbon in Holocene sediments provided data to calculate an organic carbon budget for the Laptev Sea continental margin. Mean Holocene accumulation rates in the inner Laptev Sea vary between 0.14 and 2.7 g C cm⁻² ky⁻¹; maximum values occur close to the Lena River delta. Seawards, the mean accumulation rates decrease from 0.43 to 0.02 g C cm⁻² ky⁻¹. The organic matter is predominantly of terrigenous origin. About 0.9 × 10⁶ t year⁻¹ of organic carbon are buried in the Laptev Sea, and 0.25 × 10⁶ t year⁻¹ on the continental slope. Between about 8.5 and 9 ka, major changes in supply of terrigenous and marine organic carbon occur, related to changes in coastal erosion, Siberian river discharge, and/or Atlantic water inflow along the Eurasian continental margin. Received: 26 October 1998 / Revision accepted: 15 June 1999     

Geochemistry of salt marsh sediments deposited during simulated sea-level rise and consequences for recent and Holocene coastal development of NW Germany

De-embankment in the salt marshes of the island of Langeoog was carried out in 2004, thereby inducing an artificial transgression within an area of 2.2 km². Material from three suspended matter traps (SMTs) located along a N–S transect was collected monthly between January 2006 and February 2007. Besides geochemical (major and trace elements) and grain-size analyses, the duration and height of water cover were continuously measured by pressure gauges during the sampling period at two sites, thus revealing inundation frequency (max. 280 year⁻¹) and level (max. 2.4 m). Generally, the silt-dominated SMT material exhibits a geochemical composition similar to that of suspended particulate matter from the adjacent Wadden Sea. However, distinctly increasing enrichments of TOC, P, Mn and Mo from the shoreline towards the higher salt marsh clearly indicate fractionation processes during material transport. Geochemical comparison with older Holocene coastal deposits reveals a mixture of brackish and tidal flat sediments, thus reflecting an early stage of sea-level rise and the development from a terrestrial towards a marine-dominated system. Sedimentation rates are higher than the local sea-level rise, as revealed by vertical salt marsh growth. Storm surges deliver the highest amounts of sediment and play an important role in salt marsh accumulation within the study area. Average accumulation rates of TOC (780 t year⁻¹), P (54 t year⁻¹) and Mn (5.2 t year⁻¹) in the de-embanked area suggest that the former sand-dominated sediments currently receive significant amounts of reactive organic-rich material, thus fostering biogeochemical cycling.     

Active tectonic morphology and submarine deformation of the northern Gulf of Eilat/Aqaba from analyses of multibeam data

A high-resolution marine geophysical study was conducted during October-November 2006 in the northern Gulf of Aqaba/Eilat, providing the first multibeam imaging of the seafloor across the entire gulf head spanning both Israeli and Jordanian territorial waters. Analyses of the seafloor morphology show that the gulf head can be subdivided into the Eilat and Aqaba subbasins separated by the north-south-trending Ayla high. The Aqaba submarine basin appears starved of sediment supply, apparently causing erosion and a landward retreat of the shelf edge. Along the eastern border of this subbasin, the shelf is largely absent and its margin is influenced by the Aqaba Fault zone that forms a steep slope partially covered by sedimentary fan deltas from the adjacent ephemeral drainages. The Eilat subbasin, west of the Ayla high, receives a large amount of sediment derived from the extensive drainage basins of the Arava Valley (Wadi ’Arabah) and Yutim River to the north–northeast. These sediments and those entering from canyons on the south-western border of this subbasin are transported to the deep basin by turbidity currents and gravity slides, forming the Arava submarine fan. Large detached blocks and collapsed walls of submarine canyons and the western gulf margin indicate that mass wasting may be triggered by seismic activity. Seafloor lineaments defined by slope gradient analyses suggest that the Eilat Canyon and the boundaries of the Ayla high align along north- to northwest-striking fault systems—the Evrona Fault zone to the west and the Ayla Fault zone to the east. The shelf–slope break that lies along the 100 m isobath in the Eilat subbasin, and shallower (70–80 m isobaths) in the Aqaba subbasin, is offset by approx. 150 m along the eastern edge of the Ayla high. This offset might be the result of horizontal and vertical movements along what we call the Ayla Fault on the east side of the structure. Remnants of two marine terraces at 100 m and approx. 150 m water depths line the southwest margin of the gulf. These terraces are truncated by faulting along their northern end. Fossil coral reefs, which have a similar morphological appearance to the present-day, basin margin reefs, crop out along these deeper submarine terraces and along the shelf–slope break. One fossil reef is exposed on the shelf across the Ayla high at about 60–63 m water depth but is either covered or eroded in the adjacent subbasins. The offshore extension of the Evrona Fault offsets a fossil reef along the shelf and extends south of the canyon to linear fractures on the deep basin floor.     

Late glacial to Holocene sea-level changes in the Sea of Marmara: new evidence from high-resolution seismics and core studies

The late glacial to Holocene sedimentary record of the northern shelf of the Sea of Marmara (SoM) has been documented by detailed seismo-, chrono-, and biostratigraphic analyses using sub-bottom (Chirp) profiles and sediment cores. During MIS 3 and the main part of MIS 2 (60–15 ¹⁴C ka b.p.), disconnection from the Mediterranean and Black seas together with a dry climate resulted in a regression in the SoM, when the Sea was transformed into a brackish lake. The river incisions below 105 m water depth along the northern shelf took place during the last glacial maximum, when the lake level was modulated by stillstands at −98 and −93 m. The post-glacial freshwater transgressive stage of the Marmara ‘Lake’ occurred between 15 and 13.5 ¹⁴C ka b.p., leading to a rise in water level to −85 m by 13.0 ¹⁴C ka b.p., as evidenced by broad wave-cut terraces along the northern shelf. Since 12 ¹⁴C ka b.p., high-frequency sea-level fluctuations have been identified at the SoM entrance to the Strait of İstanbul (SoI). Thus, wave-cut terraces have been recorded at water depths of −76 and −71 m that, according to an age model for core MD04-2750, have ages of 11.5 and 10.5 ¹⁴C ka b.p., respectively. Ancient shoreline at −65 m along the northern shelf presumably formed soon after the Younger Dryas (YD) at ca. 10.1 ¹⁴C ka b.p. Moreover, there is compelling evidence of Holocene outflow from the Sea of Marmara to the Black Sea. At the SoM entrance to the SoI, the existence of bioherms on the reflector surface together with abundant Brizalina spathulata and Protoglobulimina pupoides in a core suggests a return to higher salinities due to strong Mediterranean water incursion into the SoM at ∼8.8 ¹⁴C ka b.p. This finding is consistent with earlier suggestions that, after the YD, the Black Sea was flooded by outflow from the SoM as a result of global sea-level rise.     

Organic carbon accumulation and sulfate reduction rates in slope and basin sediments of the Ulleung Basin,East/Japan Sea

This study investigated the organic carbon accumulation rates (OCARs) and sulfate reduction rates (SRRs) in slope and basin sediments of the Ulleung Basin, East/Japan Sea. These sediments have high organic contents at depths greater than 2,000 m; this is rare for deep-sea sediments, except for those of the Black Sea and Chilean upwelling regions. The mean organic carbon to total nitrogen molar ratio was estimated to be 6.98 in the Ulleung Basin sediments, indicating that the organic matter is predominantly of marine origin. Strong organic carbon enrichment in the Ulleung Basin appears to result from high export production, and low dilution by inputs of terrestrial materials and calcium carbonate. Apparent sedimentation rates, calculated primarily from excess ²¹⁰Pb distribution below the zone of sediment mixing, varied from 0.033 to 0.116 cm year⁻¹, agreeing well with previous results for the basin. OCARs fluctuated strongly in the range of 2.06–12.5 g C m⁻² year⁻¹, these rates being four times higher at the slope sites than at the basin sites. Within the top 15 cm of the sediment, the integrated SRRs ranged from 0.72 to 1.89 mmol m⁻² day⁻¹, with rates approximately twice as high in the slope areas as in the basin areas. SRR values were consistently higher in areas of high sedimentation and of high organic carbon accumulation, correlating well with apparent sedimentation rates and OCARs. The sulfate reduction rates recorded in the basin and slope sediments of the Ulleung Basin are higher than those reported for other parts of the world, with the exception of the Peruvian and Chilean upwelling regions. This is consistent with the high organic carbon contents of surface sediments of the Ulleung Basin, suggesting enhanced organic matter fluxes.     

Past and present sedimentary activity in the Capbreton Canyon, southern Bay of Biscay

Located in the south-eastern part of the Bay of Biscay, the Capbreton Canyon incises the continental shelf up to the 30 m isobath contour, and acts as a natural conduit for continental and shelf-derived sediments. EM1000 multibeam bathymetry shows two main features characterising the canyon — a deeply entrenched meandering channel, bordered by fluvial-like terraces constituting large sediment traps. A dataset of cores and seismic profiles together with a multibeam bathymetry map has enabled the characterisation of recent sedimentary activity in the axial channel and on the terraces. Data analysis evidenced the major role of the canyon head in recent sediment dynamics. This part of the canyon is a temporary reservoir for sediments, accumulated by coastal hydrodynamic processes. Exceptional climatic, tectonic or hydrodynamic events can mobilise the sediments and generate gravity-driven flows. Under the present-day sea-level highstand conditions, these flows are not powerful enough to bring their bedload to the deep sea, and are confined mainly to the upper part of the canyon. Turbidity currents model the axial channel pathway and are at the origin of terrace formation. Terraces in the Capbreton Canyon are not typical but rather are reduced to confined levees. Three factors control the vertical growth of a terrace: (1) the amount of overspilled sediments brought by turbidity currents, (2) hemipelagic sedimentation and (3) terrace height. The amount of sediment spilling over a terrace decreases with increased terrace elevation. Concurrently, the proportion of hemipelagic fallout depositing on a terrace increases. Terraces are considered to be fossil when the height of the terrace prevents further deposition by overspilling. The terraces studied in this paper are interpreted as having formed during the Holocene, implying that the sediment dynamics of the Capbreton Canyon is continuous through time. Highstand periods differ from lowstand periods because they show a decrease in the energy of erosive processes. Temporal variations in erosive and depositional processes in the canyon are controlled by the Adour River, which delivers large amounts of sediment to the system.     

Nutrient fluxes from deep sediment support nutrient budget in the oligotrophic waters of the Gulf of Aqaba

The role of deep sediment in supporting nutrient budget in the Gulf of Aqaba has been investigated by estimating the flux of inorganic nitrogen, phosphate and silicate. Fluxes were calculated directly by pore water profiles and indirectly by chamber incubations carried out onboard the RV Meteor cruise. The results showed that maximum potential fluxes calculated by chamber incubations were higher than those calculated by porewater profiles for all nutrients (6.4–28.5 fold). This has been attributed to the additional flux due to bioturbation and flux from advective porewater exchange in the case of chamber incubation, while porewater fluxes represent diffusive ones. Using a rough estimation considering flux results in addition to the sediment area and water mass of the Gulf of Aqaba, we estimate that 3.3 × 10⁵, 6.4 × 10⁴ and 6.5 × 10⁶ kg year⁻¹ of inorganic nitrogen, phosphate and silicate respectively are effused from deep sediments to the water column. This quanitity would certainly support the primary productivity in the oligotrophic water in the Gulf of Aqaba.     

Geology of the Miami Terrace and its paleo-oceanographic implications

The Miami Terrace is a drowned early to middle Tertiary carbonate platform, the outer margin of which has been deeply incised by submarine erosion subsequent to deposition of the limestone terrace. This interpretation is based on the study of high-resolution seismic reflection profiles, rock dredge samples, observations from deep-diving submersibles, and correlation with drill-hole data. The karstic upper terrace (200–375 m) yields limestones and dolostones of early middle Miocene age that have shallow-shelf affinities. Truncated beds of an eastward-dipping deeper-water slope facies are exposed on the upper surface of the erosional lower terrace at 600–700 m. The upper and lower terraces are separated by a discontinuous ridge, probably a drowned Miocene, or post-Miocene bank margin complex. Both terraces and the ridge are capped by dense conglomeratic phosphorites and phosphatic limestones. Phosphorite nodules are more common on the lower terrace whereas the upper terrace yields large phosphorite slabs as well as shark's teeth and bones of marine mammals.

Petrographic study of dredged and submersible-sampled rocks shows that two or more episodes of phosphatization took place intermittent with erosion, grain rounding, reworking and redeposition. Early stages of phosphatization appear to be selective, replacing the more unstable carbonate minerals first, while later stages are nonselective. The origin of most of the phosphorites is the diagenetic replacement of calcium carbonate by francolite.

The karst surface of the upper terrace appears to have been produced by subaerial exposure in the middle to late Miocene as evidenced by shallow-water components in the rocks of the upper terrace plus considerations of local subsidence and eustatic sea-level curves. The erosional lower terrace, 200–300 m deeper than the upper terrace, would have been too deep to have been produced by subaerial or wave erosion. An erosional hiatus of middle Miocene age in JOIDES drill holes on the Blake Plateau indicates that bottom-current velocities in this area increased over this interval. The formation of the lower erosional terrace is related to increased flow of the Gulf Stream system (Florida Current) and bioerosion concurrent with the tectonic uplift and oceanographic closure of the western Caribbean in mid-Miocene time.

The bathymetry, petrology, structure and paleontology of the Miami Terrace, along with correlative data from adjacent areas, argue that a more active Gulf Stream system began as early as the middle Miocene (10.5–16 m.y.B.P.) rather than the early to middle Pliocene (3.5–4.0 m.y.B.P.) as previously suggested.     

On the genesis of some bottom and coastal features in the Eastern Gulf of Finland

An investigation undertaken recently by the Division of Regional Geoecology and Marine Geology of the Karpinsky All-Russian Research Geological Institute in the coastal zones of the Eastern Gulf of Finland allowed finding some specific relief forms of both near-shore bottom topography and shoreline shape. First of all, among the most interesting objects, the sand ridges on the surface of submarine terrace (between Repino locality and Cape Lautaranta) should be mentioned. These ridges are elongated at an angle to the shoreline and are located beyond the limits of wave action. The other interesting morphological type is represented by longshore sand waves up to some hundreds of meters long and some tens of meters wide near the Bol’shaya Izhora locality. Longshore sand waves move along the southern coast of the gulf, this causing alteration of erosion and accretion zones and leading to formation and degradation of the sand spits. Shore-face-connected ridges are believed to develop under the action of drift currents generated during the passage of deep west cyclones. It is shown that the ridge turned toward the current gives rise to a convergence of the cross-shore flows over the crest and provokes a shift of the maximum velocity toward the front side of the structure. Associated changes in sediment discharges result in accumulation and growth of the ridge. The origin of wavelike features in the shoreline contour (longshore sand waves) is due to a very oblique wave approach caused by predominance of the west winds blowing along the axis of the gulf. Under these conditions a small perturbation of the shoreline contour is shown to manifest a trend to increase with time.     

Analysis of trophic networks and carbon flows in south-eastern Baltic coastal ecosystems

Carbon flows in five south-eastern Baltic coastal ecosystems (Puck Bay, Curonian Lagoon, Lithuanian coast, Gulf of Riga coast and Pärnu Bay) were compared on the basis of ECOPATH models using 12 common functional groups. The studied systems ranged from the hypertrophic Curonian Lagoon to the mesotrophic Gulf of Riga coast. Interestingly, we found that macrophytes were not consumed by grazers, but rather channelled into the detritus food chain. In all ecosystems fisheries had far reaching impacts on their target species and on the food-web in general. In particular, benthic food-webs were partly affected by indirect fisheries effects. For example, fisheries tend to change the biomass of piscivorous fish, causing a cascading effect on benthivorous fish and macrozoobenthos. These cascades are ecosystem specific and need to be considered when using benthic invertebrates as productivity and eutrophication indicators. Odum’s maturity attributes allowed a ranking of costal ecosystems according to their maturity. Namely, the community development decreased in the following order: Pärnu Bay > Gulf of Riga coast > Lithuanian coast > Puck Bay > Curonian Lagoon.     

Possibility of recent changes in vertical distribution and size composition of chlorophyll-a in the western North Pacific region

Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a (Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season, as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4 and 2.3% year⁻¹ in the subtropical area along 137°E (STA₁₃₇) during 1972 to 1997 and in the Kuroshio Extension area along 175°E (KEA₁₇₅) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year⁻¹ in STA₁₃₇ and KEA₁₇₅; and (3) decreasing linear trend of larger-size Chl-a (>3 μm) by 0.1 and 2.5% year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. Water density (σ _θ ) at 75 m depth had also decreased by 0.006 and 0.05 year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. The ratio of biogenic opal to biogenic CaCO₃ in the sinking flux decreased by 0.015 year⁻¹ in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density of surface water caused by warming in the western North Pacific, especially in the summer.     

Carbonate slope morphology revealing sediment transfer from bank-to-slope (Little Bahama Bank,Bahamas)

New high-quality multibeam and high-resolution seismic data reveal new observations on sediment transfer and distribution and margin morphometrics in the uppermost slope of Northeastern Little Bahama Bank between 20 and 300 m water depth. The echofacies/backscatter facies show an alongslope sediment distribution forming successive strips. The upper part of the uppermost slope corresponds to the alternation of several submerged coral terraces and escarpments that could be related to Late Quaternary sea-level variations. The terraces could either be related to periods of stagnating sea-level or slow-down in sea-level change and therefore increased erosion by waves, or periods of accelerated sea-level rise since the Last Glacial Maximum. Terraces could therefore be related to coral construction and drowing. The medium part corresponds to the marginal escarpment, a steep cemented area. The lower part of the uppermost slope shows a discontinuous Holocene sediment wedge with varying thickness between 0 and 35 m. It is separated from the upper part by a zone of well-cemented seafloor associated with the marginal escarpment. Passing cold fronts result in sediment export caused by density cascading. The associated sediment fall-out and convective sedimentation can generate density currents that form this wedge and eventually flow through linear structures on the upper slope. The survey reveals the presence of recently active channels that extend over the entire uppermost slope and interrupt the wedge. The channels connect shallow tidal channels to submarine valleys connected to the proximal part of canyons. They directly feed the canyons with platform-derived sediment forming low-density turbidity currents and could supply the deepest part of the system with coarse-grained sediment directly exported from the carbonate platform.     

Reflection of a long wave from an underwater slope

Reflection of long sea waves from an underwater slope described by a power law is studied within the shallow water theory. The slope is connected with the flat bottom. This model allows us to estimate the roles of a pointwise reflection from the inflection point of the bottom profile and distributed reflection at the underwater slope. The case of the underwater slope described by the so-called nonreflecting beach (h(x) ∼ x ^4/3, where h is the depth of the basin and x is the coordinate) when the wave is reflected only from the inflection point (pointwise reflection) is specially considered. The reflection and transmission coefficients over the bottom topography were calculated, and it was shown that the sum of the squared absolute values of these values differs from unity for all profiles except the nonreflecting one. This difference is related to the distributed re-reflections (resonances) over the underwater slope that lead to the deviations in the wave height from the known Green’s law.     

Effect of solid to solution ratio on biogenic silica determination in coastal sediments

The method of DeMaster (1981) for measuring biogenic silica (BSi) in marine sediments was modified. We found a considerable effect of the solid to solution (S/S) ratio on BSi determination in coastal sediments. The BSi contents determined by DeMaster’s method were overestimated due to the contribution of clay mineral-derived extractable Si at a low S/S ratio (<1 g l⁻¹), and incomplete recovery of BSi was observed due to incomplete extraction when using a high S/S ratio (>2 g l⁻¹). For BSi analysis of coastal sediment samples, the BSi content of representative samples must be measured using various S/S ratios to determine the appropriate S/S ratio in order to minimize the contribution of extractable Si derived from clay minerals and to obtain sufficiently efficient extraction with 1% Na₂CO₃ before actual sample measurement. One way to determine the appropriate S/S ratio is to use artificial sediment which has a theoretical Si and clay mineral content similar to the sediment sample composition. Using artificial sediment, the S/S ratio of 2 g l⁻¹ seems appropriate for measuring the BSi content of the coastal sediments investigated in this study, because 99.6% recovery can be achieved.     

Growth of a post-Little Ice Age submarine fan, Glacier Bay, Alaska

A small Holocene fan is forming where Queen Inlet, a hanging valley, enters West Arm fjord, Glacier Bay, Alaska. Queen fan formed in the last 80 years following retreat of the Little Ice Age glacier that filled Glacier Bay about 200 yr BP. It was built mainly by a turbidite system originating from Carroll Glacier delta, as the delta formed in the early 1900s at the head of Queen Inlet. The Late Holocene Queen fan is comparable to large Pleistocene fans that formed in the Gulf of Alaska and differs from trough-mouth fans formed by cooler climate glacier systems. Received: 7 January 1999 / Revision received: 3 June 1999     

Characteristics of coastal-trapped waves induced by typhoon along the southeast coast of Honshu,Japan

Mooring observations using ADCP, electromagnetic current meters and thermometers were performed to clarify the vertical and horizontal structure of coastal-trapped waves (CTWs) on continental shelf and slope on the eastern side of Sagami Bay, Japan, in August and September 2003. A strong inflow associated with CTW caused by Typhoon 0315 (CTW15) was observed with remarkable downwelling. The maximum current due to CTW15 was over 100 cm s⁻¹, confined to the upper layer shallower than 90 m. The CTW (CTW10) induced by Typhoon 0310, was associated with the coastal upwelling and maximum outflow was 33 cm s⁻¹; the currents were extended near the bottom at 230 m depth. Remarkable discrepancies were found between the current structures of CTWs. CTW15 was explained by superposing the second CTW mode on the first CTW mode, whereas CTW10 was explained by the first CTW mode. The generation and propagation processes of both CTWs were reproduced by numerical experiments using a three-dimensional level model. The model results indicated that the difference of modal characteristics between CTW15 and CTW10 already exists in the CTW generation region and are due to difference of the wind direction, i.e., the typhoon’s path.     

Morpholithodynamic processes in the coastal zone of the Anapa spit barrier

The results of field studies of the beach dynamics and the continental slope (over the depth range from 0 to 5 m) of the Anapa spit barrier that were carried out in 2002–2005 using ten lateral profiles are presented. The analysis of the location of the submarine ridges based on the data of 1992 up to a depth of 11 m has shown that the configuration thereof facilitates the transport of sediments to the southeast, thus bypassing Cape Anapa. No resultant accumulation of beach-forming sediments on the southeastern flank of the spit barrier occurs within the submarine slope bordering the high coast, thus provoking the active erosion of the town beach over the last 25–30 years. The main reasons for this are the tectonic deformation of the coastal region and the submarine slope between the harbor and the central part of the town beach, as well as the change in the azimuth orientation of the resultant waves from 135° in the 1960s–1970s to 210° over the past decade. The relatively stable coast and the regions of intense erosion of the accumulative body of the Anapa spit barrier were revealed on the basis of the measurements and the analysis of the topographic data.     

西沙群岛宣德环礁的精细水下地貌组合特征及其成因机制

海底地形地貌及类型分布特征对指示区域地质构造影响、海平面升降、海洋水动力等有重要意义。本文通过侧扫声呐、单波束测深、表层沉积物取样等方法,分析了西沙群岛宣德环礁精细水下地貌组合特征,并探讨了其成因机制。结果表明:（1）宣德环礁为残缺型环礁类型,中部为潟湖沉积,礁盘之间形成西沙洲口门、“红草门”、环礁西缺口和环礁南缺口等4处水深超过60 m的深水口门,并首次识别了西沙洲口门;（2）宣德环礁水下地貌类型可划分为3级11类地貌类型。研究区的沙波及槽沟等动力地貌单元显示,宣德环礁浅水区海底特征地貌由盛行季风和波浪场所控制,深水口门形成的潮汐通道水体为塑造宣德环礁潟湖区动力地貌的主要因素。研究区东南部向海坡存在6级水下阶地,通过对比南海珊瑚礁阶地特征,宣德环礁向海坡阶地成因很可能是全球海平面变化和地壳沉降的共同作用。     

Egg production rate of the copepod <Emphasis Type="Italic">Calanus sinicus</Emphasis> off the Korean coast of the Yellow Sea during spring

The egg production rate (EPR) of Calanus sinicus was measured from March 2007 to April 2010 at three stations along the Korean coast of the Yellow Sea (in coastal waters off Saemangum, Yeongheungdo, and Asan Bay) to estimate in situ maximum egg production rate (MEPR) and to understand whether the females were limited in their growth or fecundity in the field. The mean EPR of C. sinicus at each sampling date ranged from 10.3–34.9 eggs female⁻¹ d⁻¹ (mean 23.4 eggs female⁻¹ d⁻¹), and the EPR of individual copepods ranged from 0–81 eggs female⁻¹ d⁻¹. The mean EPR was positively correlated with the body weight of female copepods. The MEPR at each sampling date ranged from 40–81 eggs female⁻¹ d⁻¹ (mean 50.4 eggs female⁻¹ d⁻¹). Over 84% of eggs spawned hatched successfully. The weight-specific growth rate (WSGR) ranged from 0.038–0.111 d⁻¹ (mean 0.082 d⁻¹), indicating that 3.8–11.1% of the carbon in an adult female was produced daily as female growth. The WSGR was negatively correlated with water temperature. The ratio of mean EPR to observed mean MEPR ranged from 20–70% (mean 46%), indicating that ∼54% of a female’s growth might be limited in the field. We suggest that the ratio of observed EPR to mean MEPR of copepod can be applied to understand how the copepod responds to environmental changes, as well as EPR and hatching success.     

Shallow-water longshore drift-fed submarine fan deposition (Moisie River Delta, Eastern Canada)

Submarine canyons and associated submarine fans are in some cases located at the end of a littoral cell where they act as conduits for the transfer of eroded terrigenous sediments to the marine environment. Such fans are generally found in deep-water settings at >500 m water depth. Offshore the Moisie River Delta (NW Gulf of St. Lawrence, Eastern Canada), high-resolution multibeam bathymetry and seismic data led to the discovery of an unusually shallow submarine fan (≤60 m) located at the end of a littoral cell. Sediment is transported westward on the shallow coastal shelf, as demonstrated by the downcurrent displacement of oblique nearshore sandbars where the shelf narrows to less than 1 km. The steep slope near the end of the littoral cell is incised by a channel that feeds a submarine fan composed of smaller channels and depositional lobes. According to existing Holocene evolution models for the region, the fan formed within the last 5,000 years. Its evolution is largely due to the transport of sediment by longshore drift. Multibeam echosounder and seismic data also reveal that the gravity-driven accretion of the submarine fan is characterized mainly by two processes, i.e., frequent small-scale, downslope migration of sandwaves on the slope, and more episodic slumping/turbidity-current activity in the deeper part of the fan. This study documents that, besides their common deep-water location, smaller-scale submarine fans can occur also in very shallow water, implying that they could be more frequent than previously thought both in modern environments and in the rock record.