Phytoplankton growth response to wind induced regional upwelling occurring around the Izu Islands off Japan

From frequent field observations performed in coastal waters around the Izu Islands, Japan, a clear regional upwelling associated with the wind was detected baside Niijima Island. Nutrient supply by the upwelling into the euphotic zone was confirmed, and the subsequent phytoplankton growth supported by the upwelled nutrients was evaluated. The upwelling and the nutrient supply occurred within a day over an area ofca. 400 km², and phytoplankton growth response occurred only a few days after the upwelling. Such regional upwelling is considered to be one of the major mechanisms supporting the high productivity of coastal waters.Contribution number 423 from the Shimoda Marine Research Center, University of Tsukuba.     

Rare earth elements and Opal/CaCO<Subscript>3</Subscript> ratio of sinking particles observed with a time-series sediment trap at the mouth of Tokyo Bay

A time-series sediment trap was deployed from December 1994 to February 2002 at the mouth of Tokyo Bay (35°03′ N, 139°40′ E; water depth, 850 m). Sinking particles were obtained with a time interval of one week at a depth of approximately 100 m above the sea floor. Observed total mass fluxes varied from 3.3 to 226.7 g/m²/day with an average of 28.0 g/m²/day. Concentrations of rare earth elements, Al, Ca and Si in particulate materials were measured. The combustible fraction at 450°C is assumed to be equivalent to the organic matter content. Contents of biogenic materials, namely organic matter, opal and calcium carbonate, were about 30% and the content of lithogenic material was about 70%. Using La/Yb ratios of particles from the sediment trap and Tama-gawa River and surface sediment of Tokyo Bay, it was estimated that about 50% of the lithogenic particles collected in the sediment trap at the mouth of Tokyo Bay originated from resuspended surface sediment in Tokyo Bay. An increasing trend of Opal/CaCO₃ ratio in the sinking particles was found in the spring season. It is suggested that the relative increase of diatoms is due to the decreasing dissolved inorganic nitrogen input into Tokyo Bay.     

Measurements of vertical air temperature gradients with dipmeter

By means of measuring the dips of horizon with a Pulfrich dipmeter, vertical air temperature gradients near the sea surface were obtained with an accuracy of ca. ±0.01°C/m, much better than a conventional method with an array of temperature sensors. The additional advantage of this technique was that the measurements were made on board a ship underway, consequently data from wide oceanic areas could be accumulated rather quickly and easily. From the results of dip measurements at 125 stations on two cruises of the T/V Oshoro Maru of the Hokkaido University, extending from the Bering Sea to the south of Australia, the temperature gradients were computed with a new formula with an assumption that the refractive index of air varied with a height only. It was found that, in the northern North Pacific Ocean, vertical air temperature gradients were positive, while in the subtropical and tropical Pacific Ocean both the negative and positive gradients were observed. Generally, in the same sea region, the temperature profiles had the similar form, irrespective of air-sea temperature differences.     

Diatom Assemblage and Productivity Changes during the Last 340,000 Years in the Subarctic Pacific

Diatoms represent the major part of the microfossils preserved in the subarctic Pacific sediments. During the warm climate intervals the diatom accumulation rate (DAR) tended to increase, whereas it tended to decrease during the cold intervals. Principal component (PC) analysis of the fossil diatom assemblages in Piston Core KH99-3 ES samples from the subarctic Pacific was carried out to investigate the paleoceanographic conditions of the area. PC1 (59.9% of the total variance) was represented by Neodenticula seminae, a characteristic species representing the high nutrient concentrations, which dominated during the interglacial periods. The DAR and PC changes can be attributed to a global origin that is influenced by the nutrient change due to intermediate water change and to a local one that is explained by the change of upwelling region. The analysis of PC2 (17.1% of the total variance) indicates the change of water mass in the western subarctic Pacific. During Marine Isotope Stages (MIS) 2 and 3, the western subarctic Pacific region was significantly influenced by the sea-ice, which may have been derived from the coastal region or a proximal marginal sea. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chlorophyll a Biomass of Netplankton in Surface Waters in the Pacific Sector of the Southern Ocean in Austral Summer

Chlorophyll a of total and particles retained on 30 μm mesh plankton net were both determined in surface waters along two cruise tracks ranging from the Subtropical water to the marginal ice zone in the Pacific sector of the Southern Ocean in austral summer. Total surface chlorophyll a in the study area was mostly less than 1 μg chl a 1⁻¹, and showed distributions with no obvious trend associated with different waters masses of the Antarctic and the Subantarctic, although total chlorophyll a concentrations changed greatly within each water mass. Particularly low concentrations of chlorophyll a were detected in the marginal ice zone. Chlorophyll a contained in 30 μm netplankton made up 5∼60% of total chlorophyll a: large near the marginal ice zone and becoming small with travel towards the north. High percentage shares of netplankton chlorophyll a were confirmed even in low total chlorophyll a concentrations in summer in the Southern Ocean. A positive relation was observed between the percentage of 30 μm netplankton and the “average total chlorophyll a”, although there was great scatter. This revised version was published online in August 2006 with corrections to the Cover Date.     

Occurrence and seasonal variations of algal toxins in water, phytoplankton and shellfish from North Stradbroke Island, Queensland, Australia

A number of marine microalgae are known to produce toxins that can accumulate in shellfish and when eaten, lead to toxic and potentially fatal reactions in humans. This paper reports on the occurrence and seasonal variations of algal toxins in the waters, phytoplankton and shellfish of Southeast Queensland, Australia. These algal toxins include okadaic acid (OA), domoic acid (DA), gymnodimine (GD), pectenotoxin-2 (PTX-2) and pectenotoxin-2-seco acid (PTX-2-SA), which were detected in the sampled shellfish and phytoplankton, via HPLC-MS/MS. Dissolved OA, PTX-2 and GD were also detected in the samples collected from the water column. This was the first occasion that DA and GD have been reported in shellfish, phytoplankton and the water column in Queensland waters. Phytoplankton tows contained both the toxic Dinophysis and Pseudo-nitzschia algae species, and are suspected of being the most likely producers of the OA, PTX-2s and DA found in shellfish of this area. The number of cells, however, did not correlate with the amount of toxins present in either shellfish or phytoplankton. This indicates that toxin production by algae varies with time and the species present and that number of cells alone cannot be used as an indicator for the presence of toxins. The presence of OA and PTX-2s were more frequently seen in the summer, while DA and GD were detected throughout the year and without any obvious seasonal patterns.     

Time-series sediment trap record of alkenones from the western Sea of Okhotsk

C₃₇–C₃₉ alkenones were measured in time-series sediment trap samples collected from August 1998 to June 2000 at two depths in the seasonal sea ice region of the western Sea of Okhotsk, off Sakhalin, in order to investigate alkenone production and water-column processes in the region. Measurable export fluxes of alkenones are ranged from < 0.1 to 5.8 μg/m²/day and clearly showed that the alkenone production was restricted to autumn. In 1998, maximum export flux of alkenones occurred in September when surface water column was well stratified with low nutrients in the surface mixing layer. In the next year, the maximum flux is observed in October. Comparison between alkenone temperature and satellite based sea surface temperature (SST) shows that the estimated alkenone temperatures in August 1998 were found to be  10 °C lower than the temporal satellite SST, suggesting that alkenones are produced in surface to subsurface thermocline layers during the period. Annual mean flux of alkenones is lower in the lower traps than that of the upper traps, suggesting rapid degradation of alkenones in water column, but the U^K₃₇′ value is not significantly altered. This study indicates that U^K₃₇′ values preserved in the surface sediments off Sakhalin reflect the seasonal temperature signal of near surface water, rather than annual mean surface temperature.     

X-ray observations of PSR B1259−63 near the 2007 periastron passage

PSR B1259−63 is a 48-ms radio pulsar in a highly eccentric 3.4-yr orbit with a Be star SS 2883. Unpulsed γ-ray, X-ray and radio emission components are observed from the binary system. It is likely that the collision of the pulsar wind with the anisotropic wind of the Be star plays a crucial role in the generation of the observed non-thermal emission. The 2007 periastron passage was observed in unprecedented details with Suzaku , Swift , XMM–Newton and Chandra missions. We present here the results of this campaign and compare them with previous observations. With these data we are able, for the first time, to study the details of the spectral evolution of the source over a 2-month period of the passage of the pulsar close to the Be star. New data confirm the pre-periastron spectral hardening, with the photon index reaching a value smaller than 1.5, observed during a local flux minimum. If the observed X-ray emission is due to the inverse Compton (IC) losses of the 10-MeV electrons, then such a hard spectrum can be a result of Coulomb losses, or can be related to the existence of the low-energy cut-off in the electron spectrum. Alternatively, if the X-ray emission is a synchrotron emission of very high-energy electrons, the observed hard spectrum can be explained if the high-energy electrons are cooled by IC emission in Klein–Nishina regime. Unfortunately, the lack of simultaneous data in the TeV energy band prevents us from making a definite conclusion on the nature of the observed spectral hardening and, therefore, on the origin of the X-ray emission.