Summer Cruises Research Articles

Barrier layer in the South China Sea during summer 2000

Using temperature–salinity profiles obtained from a cruise in summer 2000, the structure and formation of the barrier layer (BL) in the South China Sea (SCS) are investigated. Fresh water flux, ocean circulation, and wind stirring are important for BL formation, depending on regions. In the eastern SCS, Philippine mountains induce heavy rainfall, resulting in a fresh water cap at the surface and the formation of a thick wide spread BL. In the northwestern basin on the lee of the Annam Cordillera range, by contrast, a rain shadow reduces fresh water flux, which along with wind-induced upwelling, prevents the BL forming. Southeast of Vietnam, a thick BL forms as the Mekong River plume is advected by the northeastward western boundary current and its offshore extension. In the southeastern basin, the surface water is mixed deeply under the strong southwesterly monsoon, unfavorable for the BL formation despite heavy rainfall. In the Luzon Strait, the east/southeastward surface Ekman drift carries fresh SCS surface water, riding on the intruding Kuroshio meander that carries well-mixed, warm and saline water. The vertical overlapping of these two water masses gives rise to a thick BL.

Microcystin concentrations and cell quotas in Saginaw Bay, Lake Huron

Distribution of the toxin microcystin was studied in Saginaw Bay, Lake Huron during two summer (August) cruises in 2003–2004. Intracellular microcystin concentrations averaged 1.1 μ g l− 1 (range 0.01–3.5 μ g l− 1), and extracellular concentrations averaged only 0.09 μ g l− 1 (range 0.01–0.18 μ g l− 1). Highest microcystin concentrations were found in the nearshore regions of the bay, which were shallow and had high total phosphorus concentrations. Microcystin concentrations were strongly correlated with Microcystis aeruginosa abundance (r = 0.8). M. aeruginosa abundance was strongly correlated with total phosphorus, and growth rates were negatively correlated with C:P ratio. Particulate nutrient ratios suggested that Saginaw Bay algae were severely phosphorus deficient. Microcystin cell quotas for M. aeruginosa averaged 140 fg cell− 1, and were not correlated with any environmental factor or growth rates. In Saginaw Bay, phosphorus availability primarily influences microcystin concentrations through direct control of M. aeruginosa abundance and growth rates, and not through direct control of cellular microcystin synthesis.

Size fraction and class composition of phytoplankton in the Antarctic marginal ice zone along the 140°E meridian during February–March 2003

We investigated the size fraction and pigment-derived class compositions of phytoplankton within the euphotic zone of the Antarctic marginal ice zone between 63.3°S and 66.5°S along the 140°E meridian on two consecutive cruises in the late austral summer and early austral autumn of 2003. We observed significant temporal and spatial variations in phytoplankton size and taxonomic composition, although chlorophyll a concentrations were generally below 1 μg l −1 during both periods. Microphytoplankton (>20 μm), mainly diatoms, were prominent in the euphotic zone in the southernmost area around 66.5°S during late summer. In the rest of the study area during both cruises, the phytoplankton community was dominated by pico- and nano-sized populations (<20 μm) throughout the euphotic zone. The small-size populations mostly consisted of diatoms and haptophytes, although chlorophytes were dominant in extremely cold water (−1.5°C) below the overlying warm water around 65.5°S during late summer. From late summer to early autumn, chlorophytes declined in abundance, probably due to increasing temperature within the euphotic zone (−1 to 0°C). These pico- and nano-phytoplankton-dominated populations were often accompanied by relatively high concentrations of ammonium, suggesting the active regeneration of nutrients within the small-size plankton community.

Patchiness and spatial structure of the early developmental stages of clupeiforms in the NW Mediterranean Sea

We analyse the spatial structure of early developmental stages of three ecologically important small pelagic schooling fish species in the northwestern Mediterranean Sea: the anchovy Engraulis encrasicolus, the round sardinella Sardinella aurita, and the sardine Sardina pilchardus. We used data on egg and larval abundance (arranged by development stage), hydrographic data and potential prey biomass collected during two cruises in summer and autumn 2005. Our analysis is based on the computation of Lloyd's patchiness index during the ontogeny of early developmental stages, as well as the computation of spatial auto-correlograms and cross-correlograms with environmental variables. The combined analysis allowed determination of the relative role of behavioural traits and the influence of hydrographic conditions in shaping the spatial structure of the three clupeiforms. We show that the spawning and developmental strategies of the two summer-spawning species (E. encrasicolus and S. aurita) are different. Engraulis encrasicolus has relatively low patchiness for all early developmental stages, while the importance of trophic variables in determining spatial structure increases during development. Sardinella aurita spawns in a trophically favourable environment and the patchiness of its early developmental stages increases for older larvae, becoming decoupled from environmental variables. The autumn spawned S. pilchardus eggs and larvae showed a development strategy similar to S. aurita, with limited importance of environmental variables in determining their patchiness.

The influence of upwelling, coastal currents and water temperature on the distribution of the red tide dinoflagellate, Noctiluca scintillans, along the east coast of Australia

Quasi-synoptic surveys along the east coast of Australia between 28 and 34°S show that the heterotrophic dinoflagellate, Noctiluca scintillans, occurs along this entire stretch of the coast. Areas of relatively high abundance of Noctiluca were observed downstream of regions predisposed to current-induced upwellings as a consequence of alongshore topographic variations. High-resolution temporal and spatial sampling of upwelling events showed that Noctiluca was abundant (up to 28 cells l−1) within mature upwelled waters. A high proportion (>80%) of fed Noctiluca cells (cells with prey in their vacuoles) was observed in the mature upwelled waters indicating that the observed increase in abundance of Noctiluca was associated with increased feeding activity. The absolute abundance of Noctiluca in upwelled waters was, however, found to vary from one upwelling location to another and between seasons. In particular, highest abundances of Noctiluca were recorded south of 31.5°S, where the East Australian Current (EAC) characteristically separates from the coast. The high abundances partly arise from southward advection and retention of the Noctiluca cells, and partly from upwelling inshore of the separated EAC driven by cross-shelf boundary layer fluxes. The temperature of the EAC was also found to influence absolute abundances. Surface water temperatures during our summer cruise were anomalously high due to a strong La Nina phase, and up to 4°C warmer than during our spring cruise. We found that the warmer surface water temperatures were associated with relatively lower average abundances of Noctiluca in the near shore zone.

Population structure, distribution and abundance patterns of the patagonian smoothhound Mustelus schmitti Springer, 1939 (Chondrichthyes, Elasmobranchii, Triakidae) in the rio de La Plata and inner continental shelf , sw Atlantic ocean (34º30'-39º30'S)

A total number of 4824 Mustelus schmitti was sampled. Females ranged from 25 to 93 cm in spring and from 28 to 90 cm in summer. Males ranged from 34 to 82 and from 28 to 77 cm, respectively. Length composition of the population showed significant differences between spring and summer being females larger than males. Total length distribution did not show significant differences between cruises. Males density varied significantly between cruises while for the females no significant variation was observed. In the spring cruise, both sexes occurred at depths lower than 50 m. Females occurred in the whole area with adult occurrence only above 35°30'S. Mature males occurred throughout the area, immature males occurring in two trawls in Samborombón Bay. The summer cruise showed a discontinuous distribution of the species along the study area resulting in spatial segregation in two groups with immature females predominating in both of them.

Observations of the Mediterranean Undercurrent and eddies in the Gulf of Cadiz during 2001

The North Atlantic is strongly influenced by the presence of a high salinity and temperature water mass – the Mediterranean Water (MW) – lying at intermediate levels. A detailed field survey in the region around the Portimão Canyon, which constitutes the first large canyon that the Mediterranean Undercurrent encounters downstream of the Strait of Gibraltar, has been repeated in three different seasonal conditions (winter, spring and summer) of the year 2001, in the frame of Project MEDTOP. This paper is based on the observations undertaken during MEDTOP and focus on relevant aspects of the thermohaline and velocity fields associated with the Mediterranean Undercurrent and the associated eddies, bringing further evidence of hypotheses presented in previous work on the dynamical behaviour of the Mediterranean Outflow and its intra-annual variability, and describing new observations of meddy formation and subsequent evolution in the centre of the Gulf of Cadiz. The analysis of the CTD data at the MW levels has shown the presence of four MW cores: the Upper and Lower Cores (centred at about 800 and 1200 m), the Shallow Core (between 400 and 600 m) and, in the region close to the Portimão Canyon, a core with higher density than the classical Lower Core at depths between 1300 and 1600 m. The analysis of the RAFOS floats trajectories has shown the Upper and Lower Cores flowing independently along the continental slope, the Upper Core reaching systematically higher velocities than the Lower Core. Within the meddies, there was evidence of a weak vertical coherence of the Cores in the early stages of the eddy life, and a tendency for acquiring a solid-body rotation as they evolve away from their source. The RAFOS floats evidenced the formation of MW eddies at three sites off the Portuguese coast: in Portimão Canyon, off Cape St. Vincent and in the Estremadura Promontory. The period of eddy generation could be quantified within the range 45–60 days. The comparison between the winter and summer cruises has confirmed some aspects of the Mediterranean outflow which had been identified in previous data sets, namely the higher temperature and salinity values, the broader lateral extension and the higher velocities of the outflow in winter relative to summer values.

Reprint of “Seasonal and daily variation of mercury evasion at coastal and off shore sites from the Mediterranean Sea”

Dissolved gaseous mercury (DGM) was measured continuously using two newly developed techniques and a manual technique. The continuous techniques were based on the equilibrium between the aqueous and gaseous phase (DGM = Hg extr / H', Hg extr is the measured mercury concentration in the gas phase, H' is the Henry's Law coefficient at the desired temperature). In order to calculate the annual mercury evasion from the Mediterranean Sea, diurnal and seasonal measurements of DGM, total gaseous mercury in air (TGM), water temperature and wind speed were performed. During August 2003, March–April 2004 and October–November 2004 measurements of these parameters were conducted on board the RV Urania. The continuous measurements of DGM showed a diurnal variation in concentration, at both coastal and off shore sites, with higher concentrations during daytime than nighttime. The concentration difference could be as large as 130 fM between day and night. The degree of saturation was calculated directly from the measurements, S = Hg extr / TGM and was found to vary between the different seasons. The highest average degree of saturation (850%) and the largest variation in saturation (600–1150%) was observed during the summer. The spring showed the lowest variation (260–360%) and the lowest average degree of saturation (320%). The autumn also showed a large variation in saturation (500–1070%) but a lower average (740%) compared to the summer cruise. This might be explained by the temperature difference between the different seasons, since that parameter varied the most. The flux from the sea surface was calculated using the gas exchange model developed by Nightingale et al. [Nightingale, P.D., Malin, G., Law, C.S., Watson, A.J., Liss, P.S., Liddicoat, M.I., Boutin, J., Upstill-Goddard, R. C., 2000. In situ evaluation of air–sea gas exchange parameterization using novel conservative and volatile tracers. Global Biogeochemical Cycles, 14(1):373–387]. The evasion varied between the different seasons with the highest evasion during the autumn, 24.6 pmol m − 2 h − 1 . The summer value was estimated to 22.3 pmol m − 2 h − 1 and the spring to 7.6 pmol m − 2 h − 1 . Using this data the yearly evasion from the Mediterranean Sea surface was estimated to 77 tons.

Northwestern Weddell Sea deep outflow into the Scotia Sea during the austral summers of 2000 and 2001 estimated by inverse methods

The northward outflow of cold, dense water from the Weddell Sea into the world ocean basins plays a key role in balancing the global heat budget. We estimate the geostrophic flow patterns in the northwestern Weddell Sea using box inverse methods applied to quasi-synoptic hydrographic data collected during the Brazilian DOVETAIL 2000 and 2001 austral summer cruises. The analysis is focused on the variations of the deep Weddell Sea outflow into the Scotia Sea within boxes that bound the main deep gaps over the South Scotia Ridge. To determine the geostrophic volume transports in each box, mass, salt, and heat are conserved within neutral density layers that are not in contact with the atmosphere. Implementing the inverse model and using property anomaly equations weighted by the flow estimate uncertainty our results are consistent with those reported in the literature. A bottom triangle extrapolation method is introduced, which improves the estimated property fluxes through hydrographic sections. In the austral summer of 2000 the transports of Weddell Sea Deep Water (WSDW) through the Philip Passage, Orkney Passage, and southwestern Bruce Passage are 0.01±0.01, 1.15±0.33, and 1.03±0.23 Sv (1 Sv=10 6 m 3 s −1, >0 is northward), respectively. After extrapolation within bottom triangles these transports increase to 0.12±0.03, 3.48±1.81, and 1.20±2.16 Sv. Analysis of the hydrographic data reveal distinct oceanographic conditions over the Philip Passage region, with evidence of mesoscale meanders, warmer and saltier Warm Deep Water (WDW) and colder WSDW observed in 2001 than in 2000. Despite these differences the WSDW transport does not present a significant variation between 2000 and 2001. The WSDW transports through the Philip Passage in 2001 are 0.012±0.001 and 0.113±0.001 Sv after extrapolation within bottom triangles. The circulation derived from the inversion in the austral summer of 2001 suggests a sharp weakening of the barotropic cyclonic flow in the Powell Basin, which may be due to northerly and northeasterly winds associated with an atmospheric low-pressure center located west of the Antarctic Peninsula. We suggest that similar variations in atmospheric forcing may explain changes in the intensity of the cyclonic flow observed in the northwestern Weddell Sea and Powell Basin.

Limitation of phytoplankton production by Si and N in the western Atlantic Ocean

Large areas of the western tropical Atlantic Ocean are influenced by the Amazon River plume, in which dissolved inorganic nitrogen (DIN) concentrations are low and nutrient N:P and N:Si ratios are lower than elemental ratios typical of phytoplankton. Accordingly, nutrient concentrations and ratios measured during winter (January to February 2001) and summer (July to August 2001) cruises in the area 2 to 14° N and 57 to 40° W suggest that DIN may limit phytoplankton growth at the majority of the 40 stations sampled. As diatoms are the dominant plankton in the Amazon plume- waters, short-term nutrient enrichment experiments were conducted to determine whether ambient N, P, or Si limited silica production rates (SiP). Results indicated that SiP were substrate limited both above and below the pycnocline at the majority of stations during both high (summer cruise) and low (winter cruise) discharge conditons. DIN concentrations also limited SiP in plumewater stations, but N additions depressed SiP at other stations, possibly using energy to take up the limiting nutrient. Finally, primary production rates were limited by ambient dissolved silicon concentrations at 9 of 13 summer stations. These results indicate the importance of dissolved silicon availability in controlling phytoplankton growth rates in a diatom-dominated river plume system.

Injury and Illness Aboard an Antarctic Cruise Ship

The objective of this study was to determine the incidence and patterns of injury and illness among passengers aboard a cruise ship in Antarctica. Demographic data on passengers were collected for all participants aboard Antarctica cruises on a single ship during the Antarctic summer cruise season of November 2004 through March 2005. Medical logs from each of 11 cruise trips were reviewed for presentation of injuries and illnesses. A total of 1057 passengers were included in the study, of which 47.4% were male. The mean age of the passengers was 54 years (+/- 16.5 years). The overall incidence rate of injury and illness was 21.7 per 1000 person-days. Motion sickness was the most common condition, comprising 42.3% of all medical encounters by the ship physician, followed by infectious diseases (17.2%) and injury (15.0%). The incidence rate of injury increased significantly with age, whereas the incidence rate of motion sickness decreased significantly with age. There was little variation in the incidence and patterns of injury and illness between genders. Most illnesses and injuries were due to the motion of the ship, and a large proportion of the passengers aboard the cruise ship in Antarctica were elderly. Injury among older passengers is of special concern.

Seasonal and daily variation of mercury evasion at coastal and off shore sites from the Mediterranean Sea

Dissolved gaseous mercury (DGM) was measured continuously using two newly developed techniques and a manual technique. The continuous techniques were based on the equilibrium between the aqueous and gaseous phase (DGM = Hg extr / H', Hg extr is the measured mercury concentration in the gas phase, H' is the Henry's Law coefficient at the desired temperature). In order to calculate the annual mercury evasion from the Mediterranean Sea, diurnal and seasonal measurements of DGM, total gaseous mercury in air (TGM), water temperature and wind speed were performed. During August 2003, March–April 2004 and October–November 2004 measurements of these parameters were conducted on board the RV Urania. The continuous measurements of DGM showed a diurnal variation in concentration, at both coastal and off shore sites, with higher concentrations during daytime than nighttime. The concentration difference could be as large as 130 fM between day and night. The degree of saturation was calculated directly from the measurements, S = Hg extr / TGM and was found to vary between the different seasons. The highest average degree of saturation (850%) and the largest variation in saturation (600–1150%) was observed during the summer. The spring showed the lowest variation (260–360%) and the lowest average degree of saturation (320%). The autumn also showed a large variation in saturation (500–1070%) but a lower average (740%) compared to the summer cruise. This might be explained by the temperature difference between the different seasons, since that parameter varied the most. The flux from the sea surface was calculated using the gas exchange model developed by Nightingale et al. [Nightingale, P.D., Malin, G., Law, C.S., Watson, A.J., Liss, P.S., Liddicoat, M.I., Boutin, J., Upstill-Goddard, R. C., 2000. In situ evaluation of air–sea gas exchange parameterization using novel conservative and volatile tracers. Global Biogeochemical Cycles, 14(1):373–387]. The evasion varied between the different seasons with the highest evasion during the autumn, 24.6 pmol m − 2 h − 1 . The summer value was estimated to 22.3 pmol m − 2 h − 1 and the spring to 7.6 pmol m − 2 h − 1 . Using this data the yearly evasion from the Mediterranean Sea surface was estimated to 77 tons.

Bio-optical signatures and biogeochemistry from intense upwelling and relaxation in coastal California

Abstract The NSF-sponsored Coastal Ocean Processes Wind Events and Shelf Transport (WEST) experiment investigates the interplay between wind-driven transport and shelf productivity; while eastern boundary shelves are characterized by high productivity due to upward fluxes of nutrients into the euphotic zone, wind forcing also represents negative physical and biological controls via offshore transport and deep (light-limiting) mixing of primary producers. Although this interaction has been well documented for eastern boundary systems generally and for California specifically, one of the primary goals of WEST was to characterize more fully the interplay between positive and negative effects of wind stress, which result in the consistently elevated biological productivity in these shelf regions. During 3 month-long summer cruises (2000–2002) we observed extremes in upwelling/relaxation, using both in situ instrumentation and remotely sensed data. Relationships between optical and physical properties were examined, with emphasis on biogeochemical implications. During 2000, the WEST region was optically dominated by phytoplankton and covarying constituents. During 2001 and 2002, periods of more intense upwelling favorable winds, we observed a transition to optical properties dominated by detrital and inorganic materials. In all years, the continental shelf break provided a natural boundary between optically distinct shelf and open ocean waters. During 2002, we obtained discrete trace-metal measurements of particulate iron and aluminum; we develop a bio-optical proxy for acetic-acid leachable iron from backscatter and fluorescence, and demonstrate that particulate iron is not well correlated to traditional upwelling proxies such as macronutrients, temperature, and salinity. We conclude that the shelf break between ca. 100 and 200 m water depth serves as a natural break point between coastal and oceanic water masses in this region, and that the elevated biomass and productivity associated with this eastern boundary current regime is dominated by these iron rich, shallow shelf waters.

The U.S. Naval Academy and Its Summer Cruises: Professionalization in the Antebellum U.S. Navy, 1845-1861

The rise of professionalism in the U.S. armed forces has been a hotly debated topic. Some, like Samuel P. Huntington, believe that it emerged in the postbellum era. Others, like William B. Skelton, assert that the U.S. Army had the ingredients of a profession before the Civil War. This study contends that the U.S. Navy also exhibited professional qualities before the Civil War. Beginning in 1845, it had a centralized school for selecting and training officers at Annapolis, Maryland. Then, at sea, as students progressed from year to year, the navy assessed almost scientifically their abilities as officer-trainees.

Export fluxes of particulate organic carbon in the Chukchi Sea: A comparative study using 234Th/ 238U disequilibria and drifting sediment traps

Large-volume sampling of 234Th and drifting sediment trap deployments were conducted as part of the 2004 Western Arctic Shelf–Basin Interactions (SBI) spring (May 15–June 23) and summer (July 17–August 26) process cruises in the Chukchi Sea. Measurements of 234Th and particulate organic carbon (POC) export fluxes were obtained at five stations during the spring cruise and four stations during the summer cruise along Barrow Canyon (BC) and along a parallel shelf-to-basin transect from East Hanna Shoal (EHS) to the Canada Basin. 234Th and POC fluxes obtained with in situ pumps and drifting sediment traps agreed to within a factor of 2 for 70% of the measurements. POC export fluxes measured with in situ pumps at 50 m along BC were similar in spring and summer (average = 14.0 ± 8.0 mmol C m − 2 day − 1 and 16.5 ± 6.5 mmol C m − 2 day − 1 , respectively), but increased from spring to summer at the EHS transect (average = 1.9 ± 1.1 mmol C m − 2 day − 1 and 19.5 ± 3.3 mmol C m − 2 day − 1 , respectively). POC fluxes measured with sediment traps at 50 m along BC were also similar in both seasons (31.3 ± 9.3 mmol C m − 2 day − 1 and 29.1 ± 14.2 mmol C m − 2 day − 1 , respectively), but were approximately twice as high as POC fluxes measured with in situ pumps. Sediment trap POC fluxes measured along the EHS transect also increased from spring to summer (3.0 ± 1.9 mmol C m − 2 day − 1 and 13.0 ± 6.4 mmol C m − 2 day − 1 , respectively), and these fluxes were similar to the POC fluxes obtained with in situ pumps. Discrepancies in POC export fluxes measured using in situ pumps and sediment traps may be reasonably explained by differences in the estimated POC/ 234Th ratios that arise from differences between the techniques, such as time-scale of measurement and size and composition of the collected particles. Despite this variability, in situ pump and sediment trap-derived POC fluxes were only significantly different at a highly productive station in BC during the spring.

Discovery of a ciliate parasitoid of euphausiids off Oregon, USA: Collinia oregonensis n. sp. (Apostomatida: Colliniidae)

An apostome ciliate, Collinia oregonensis n. sp., is reported inhabiting the cephalothorax and abdomen of 3 euphausiid species from the Oregon-Washington coast: Euphausia pacifica Hansen, 1911, Thysanoessa spinifera Holmes, 1900, and Thysanoessa gregaria G.O. Sars, 1883. This ciliate is the 7th species described for the genus Collinia and the 2nd species known to infect euphausiids. Disease progression and ciliate morphology are described using (1) modified protargol stain, (2) hematoxylin counterstained with Fast Green, and (3) Scanning Electron Microscopy (SEM). All endoparasitic developmental stages (trophont, tomont, tomitogenesis, protomite, and tomite) of C. oregonensis are astomatous and possess between 14 and 22 kineties. C. oregonensis is smaller than C. beringensis Capriulo & Small, 1986, which infects the euphausiid Thysanoessa inermis Krøyer, 1846 in the Bering Sea and which possesses between 24 and 80 kineties. The ciliate is a parasitoid because it must kill the host to complete its life cycle. Infections and mortalities in multiple host species likely reflect the virulent nature of the ciliate. Adult euphausiids infected with this parasitoid possess a swollen and bright orange cephalothorax. C. oregonensis feeds and proliferates inside euphausiids, producing fulminating infections that rupture the cephalothorax and release large numbers of tomites into the surrounding water. After several hours in the free swimming stage under shipboard conditions in the present study, the tomites adhered to each other, forming filaments. Infection rates ranged between 3 and 20% within individual euphausiid aggregations, but infected aggregations were randomly and sparingly distributed. Infected euphausiids were found at 6.7% of 316 stations sampled during 3 summer cruises. No infected euphausiids were collected in winter. Because E. pacifica and T. spinifera account for about 90% of the euphausiid standing stock in the northern California Current System, this parasitoid ciliate may have a significant impact on euphausiid population abundance, distribution and secondary productivity.

Seasonal dynamics of primary and new production in the northern South China Sea: The significance of river discharge and nutrient advection

Biochemical and productivity measurements and nutrient enrichment experiments were conducted on three cruises in summer and two cruises in winter on the shelf and the basin of the northern South China Sea (SCS) between 2001 and 2004. Phytoplankton production, in terms of depth-integrated new production (INP) or depth-integrated primary production (IPP), was higher in winter than in summer and on the shelf than in the basin. In winter, with deepening of the mixed layer, nitrate from the shallow nitracline that characterized the SCS waters was made available in the surface and supported the highest production of the year. Averaged INP measured in winter (0.25 g C m −2 d −1) was about twice the summer average (0.12 g C m −2 d −1) and was 0.19 g C m −2 d −1 on the shelf compared with 0.15 g C m −2 d −1 in the basin. In winter, average INP on the shelf was higher than the basin (0.34 versus 0.21 g C m −2 d −1); whereas in summer, averaged INP on the shelf (0.13 g C m −2 d −1) and the basin (0.11 g C m −2 d −1) were similar. While averaged IPP measured in the basin was higher in winter than in summer (0.53 versus 0.35 g C m −2 d −1), IPP on the shelf showed little temporal variation (0.82 in winter versus 0.84 g C m −2 d −1 in summer). Considerable spatial and inter-annual variation in production was measured in the shelf waters during summer, which could be linked to discharge volume and plume flow direction of the Zhujiang River. While the shelf waters in summer were mostly nitrogen starved or nitrogen and phosphorus co-limited, excessive river runoff may cause the nutritive state to shift to phosphorus deficiency. Waters with low surface salinities and high fluorescence from riverine mixing could be found extending from the Zhujiang mouth to as far as offshore southern Taiwan after a typhoon passed the northern SCS and brought heavy rainfall. Overall, both nutrient advection in winter and river discharge from the China coast in summer made new nitrogen available and shaped the dynamics of phytoplankton production in these oligotrophic waters.

Comment on “Circulation in the South China Sea during summer 2000 as obtained from observations and a generalized topography‐following ocean model” by H. Wang et al.

[1] In a recent paper, Wang et al. [2004] discuss the summer circulation in the South China Sea (SCS) using observations and a generalized topography-following ocean model. Their paper appears to be important since it is based on the only intensive observation with basin-scale coverage of the SCS in late summer. However, their results from underway observations of acoustic Doppler current profiler (ADCP) are not properly processed and may lead to misunderstanding of summer circulations of the SCS. As principal investigators of the research project of the 2000 summer cruise, we would like to present our corrections to the ADCP measurements, which result in more convincing circulation fields, and to call for attentions of properly calibration while using shipboard ADCP measurements. [2] During the cruise, along-track current measurements were conducted using an RDI 150 kHz narrow band vesselmounted acoustic Doppler current profiler (ADCP). Navigation information was provided to an RDI DAS PC by the ship’s gyrocompass and a shipboard commercial GPS for in situ data acquisition. [3] The ADCP velocity vectors at depths of both 100 and 200 m presented in Figure 5 of Wang et al. [2004] look suspicious. If comparing them with ship tracks shown in Figure 1, one can easily see that almost all velocity vectors plotted are pointing toward the port side of the research vessel. This phenomenon suggests that there had been a misalignment of the transducer with respect to the ship’s centerline that caused wrong projection of the ship’s velocity on the ADCP and led to serious systematic error in the measured currents. Therefore additional calibration after the cruise is necessary [Joyce, 1989; Pollard and Read, 1989]. It is doubtful that such calibration had been included in Figure 5 of Wang et al. [2004]. [4] There are basically two types of errors in shipboard ADCP measurements: an alignment error in the Doppler transducer/ship gyro relative to the ‘‘true’’ heading (the misalignment angle a) and a sensitivity error of the acoustic system factor (the scaling factor 1 + b), where b is relatively small but a could cause severe problems to the measurements [Joyce, 1989; Pollard and Read, 1989]. As the major error source, an error in transducer alignment and ship gyrocompass (a) will produce an apparent athwartship velocity [Joyce et al., 1986] and normally cause a systematical ‘‘offset’’ error sideward of the ship track. [5] On the basis of physics given by Joyce [1989], Pollard and Read [1989] and Joyce et al. [1986], we calibrated the same ADCP data set used by Wang et al. [2004] accordingly. Using all available bottom tracking ADCP measurements from shallow sectors of the cruise, we first estimated these calibration coefficients with bottom tracking method developed by Joyce [1989], which yields a misalignment angle of 2.34 and a scaling factor of 1.0064. Since R/V Xiangyanghong 14 was steaming at 10 knots generally, measurement error raised by the misalignment is 0.20 m s 1 roughly in the cross-track direction, which is much greater than that caused by the scaling factor (roughly 0.03 m s ). [6] Calibrations were also applied for water track mode, because that bottom tracking was not available most of the time for the cruise. In the following analysis, we assume that drifting errors derived from the gyrocompass are random in the 40-day-long cruise; hence that misalignment are basically induced by installation alignment. [7] Following Joyce [1989], the water velocities in the ‘‘true’’ north and east (x, y) coordinate frame are

Reply to comment by L. Li and R. Wu on “Circulation in the South China Sea during summer 2000 as obtained from observations and a generalized topography‐following ocean model”

Reply to comment by L. Li and R. Wu on “Circulation in the South China Sea during summer 2000 as obtained from observations and a generalized topography‐following ocean model”

Diets of herring, mackerel, and blue whiting in the Norwegian Sea in relation to Calanus finmarchicus distribution and temperature conditions

Abstract Diets of Norwegian spring-spawning herring, mackerel, and blue whiting in the Norwegian Sea are investigated in relation to the distribution of plankton and hydrographic conditions. Fish stomachs and zooplankton samples were collected during summer (June and July) cruises in 2001 and 2002. Calanus finmarchicus was the principal prey of mackerel, accounting for 53–98% of total stomach content by weight. The diet composition of herring varied depending on feeding area and availability of food under various environmental conditions. C. finmarchicus was important prey for herring only in July 2001 (about 77% by weight) in the central part of the sea and in June 2002 (about 82% by weight) near the Lofotens. In July 2002 appendicularians (Oikopleura spp.), amphipods (mainly Parathemisto abissorum), and euphausiids were important in the diet of herring, and at some stations cannibalism was observed. The main prey of blue whiting were amphipods (10–34% by weight), appendicularians (11–34%), and euphausiids (8–47%), as they usually feed deep in the water column, though C. finmarchicus was important, particularly in June 2002, when blue whiting were caught in the upper layers of the sea. Higher water temperatures indirectly affect pelagic fish through accelerated development of their prey and favourable conditions for migration farther north.