A numerical ecosystem model expressing both phosphorus and nitrogen cyclings in the pelagic system of Hiroshima Bay, Japan,
was developed in order to investigate the seasonal variations of these elements and their annual budgets. Based on the geophysical
and chemical structures of the bay, Hiroshima Bay was divided into northern and southern boxes, themselves divided into two
layers of an upper 5 m and a lower layer according to the stratification of the water column. The model consists of equations
representing all relevant physical and biological processes. The results revealed that the internal regeneration of materials
was an important source of bioavailable nutrients for phytoplankton growth in the water column. The incorporation of phytoplankton
aggregation improved the accuracy of the outputs in comparison to the observed data, especially during the stratified summer
season. The results also indicated that phosphorus limitation of phytoplankton growth occurs in the upper layer during summer
while light limitation occurs in the lower layer. In addition, physical processes such as diffusion and advection were also
important as they ensured that most of regenerated nutrients in the lower layer were transported to the upper layer. Thus,
these processes might support the high primary production and the production of oysters that are extensively cultured in this
bay. Considering the informative results obtained, the model used in this study provides a sound basis and tool to describe
the dynamics of phosphorus and nitrogen cyclings in Hiroshima Bay. 相似文献
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. 相似文献
We determined the range of the tidal variations in nutrient flux across the sediment–water interface and elucidated mechanisms of the flux variation in two estuarine intertidal flats (one sand, one mud) in northeastern Japan. Nutrient flux was measured using in situ light and dark chambers, which were incubated for 2 h, 2–6 times per day. Results showed that nutrient concentration in overlying water varied by tide and was also affected by sewage-treated water inflow. The nutrient fluxes responded quickly to the tidal variation in overlying water chemistry and the range of the variation in flux was as large as the seasonal-scale variation reported in previous studies. In the sand flat, salinity increase likely enhanced benthos respiration and led to increases in both O2 consumption and PO43− regeneration under low illumination, while benthic microalgae were likely to actively generate O2, uptake PO43− and suppress PO43− release under high illumination (>900 μmol photons m−2 s−1). Also in the mud flat, PO43− flux was related with O2 flux, although the range of temporal variation in PO43− flux was small. In both the flats, NH4+ flux was always governed by NH4+ concentration in the overlying water; either an increase in NH4+ uptake or a decrease in NH4+ release was observed as the NH4+ concentration rose due to inflow of river water or input of sewage-treated water. Although NO3− tended to be released in both tidal flats when low NO3− concentration seawater dominated, their relationship was likely to be weakened under conditions of low oxygen consumption and suppressed denitrification. It is likely that tidal variation in nutrient flux is governed more by the nutrient concentration than other factors, such as benthic biological processes, particularly in the case where nutrient concentration in the overlying water is relatively high and with wide amplitude. 相似文献
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. 相似文献
Efforts in the United States to plan or implement relocation in response to climate risks have struggled to improve material conditions for participants, to incorporate local knowledge, and to keep communities intact. Mixed methodologies of community geography provide an opportunity for dialogue and knowledge-sharing to collaboratively diagnose the challenges of climate adaptation led by communities. In this article, we advance a participatory practice model for the co-creation of knowledge initiated during a two-day workshop with members from the Biloxi-Chitimacha-Choctaw Tribe from Isle de Jean Charles in Louisiana, Yup’ik people from Newtok Village in Alaska, and researchers from the MIT Resilient Communities Lab. Building on prior scholarship of indigenizing climate change research, this article shares the experience of the workshop to support knowledge exchange and dialogue, with the goal of understanding how to build participatory and non-extractive community-academic partnerships. We reflect on the community values and principles used to guide this workshop to inform more inclusive and co-produced research partnerships, and pedagogies that can improve and assist the self-determination of groups impacted by climate change. Workshop presentations and discussions highlight interconnected themes of resources, systems & structures, regulatory imbalance, and resilience that underpin climate resettlement. We reflect on the narratives presented by members of both Indigenous tribes and NGO partners that illustrate the shortcomings of resettlement planning practices past and present as perpetuating existing inequality. In response to this structured knowledge exchange, we identify potential roles for community-academic partnerships that aim to improve the equity of existing resettlement models. We propose approaches for incorporating traditional knowledge into the pedagogy, discourse, and practice of academic planning programs.
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. 相似文献
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 UK37′ value is not significantly altered. This study indicates that UK37′ values preserved in the surface sediments off Sakhalin reflect the seasonal temperature signal of near surface water, rather than annual mean surface temperature. 相似文献
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. 相似文献