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No description available.

No description available.

No description available.

No description available.

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The marine biological carbon pump (BCP) leads to the transfer of carbon from the atmosphere to the ocean interior through the growth of photosynthetic plankton in the euphotic zone and subsequent sinking of particulate matter to depth. In the subarctic northeast Pacific Ocean, the BCP is limited by the availability of the micro-nutrient iron (Fe) in the offshore, high nutrient, low chlorophyll (HNLC) region and by the macronutrient nitrate in the coastal region. In the last decade, two atmospheric events led to anomalously high sea surface temperatures, or marine heatwaves, in 2014-2015 and 2019 that were related to changes in the phytoplankton community composition and the BCP. Given that the bioavailability of trace metals can control microbial community composition, and important rate processes related to the BCP, we studied the spatial and temporal variation in the distribution of dissolved trace metals manganese, iron, cobalt, nickel, copper, and cadmium and macronutrients nitrate, phosphate, and silicic acid from 5 stations along the Line P Time Series transect in the subarctic northeast Pacific Ocean from winter (February) and summer (August) 2012-2019. In 2014 the mixed layer shallowed by diminished winter storm mixing, resulted in lower trace metal and macronutrient concentrations, but sustained dissolved iron and net community production (NCP) in the offshore, while the coastal region biogeochemistry remained similar to previous years (2012-2013). In 2015, further mixed layer shallowing allowed for similarly diminished trace metal (most notably iron), macronutrient concentrations, and NCP in the offshore and coastal regions. The phytoplankton community in the offshore shifted towards a higher relative abundance of pico-nano size species in both 2014 and 2015, with biomass sustained in 2014 and reduced in 2015. During the second marine heatwave event in 2019, the offshore was subject to similar winter mixed layer shallowing, warming, and reduced macronutrient concentrations. In the summer, surface trace metal and macronutrient concentrations were greatly diminished, resulting in nitrate limitation in the offshore. As the oceans continue to warm in response to anthropogenic CO2, a likely consequence may be more frequent, and severe, marine heatwaves that can have internal and external effects on micro-macronutrient distributions, phytoplankton production, and the efficiency of the biological carbon pump. / Graduate

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No description available.

This study investigated trace essential metals (Cu, Zn and Cr) and non-essential metals (Pb, Cd and Hg) in water, sediment and tissues of water spinach, snake head fish and swamp eel from the Saigon River. Sampling was conducted from January to December 2004 at three sites. Three water and sediment samples, edible parts of twenty water spinach (Ipomea aquatica) samples (leaves and stems), twenty snake head fish (Channa striata) and twenty swamp eels (Monopterus albus) were collected at each site. Water, sediment and biota tissues were analysed for Cu, Zn, Cr, Pb, Cd and Hg following the method of USEPA, AOAC and NFTA. Results showed that Cu, Zn, Cr, Cd and Hg in water from the river was not higher than the maximum permitted level for protection of aquatic life by the national standards while the average Cu concentration in sediment was found to be close to the Effects range- low value and within the slightly polluted range (25- 50 ìg.g-1 dry weight). The results also showed that the river sediment was considered to be contaminated by Zn and Hg in comparison with contaminated sites in Australia and in Thailand. In water spinach, no Cu deficiency was found but Zn was accumulated. No accumulation of Cr, Cd and Hg was revealed but Pb was detectable. The results indicated that snake head and eel may have Cu deficiencies. Pb and Hg were found to be bioaccumulated in the muscle of snake head and eel at some sites on some occasions, but the levels were small. The results showed that metal in sediment liver of snake head muscle of snake head and eel water. The metals in water spinach decreased in the order Zn Cu Cr Pb Cd and Hg; in snake head the metal concentrations decreased in the order Zn Cu Cr PbHgCd and in eel as Zn Cu Cr PbCd and Hg. The ANOVA test showed no significant relationship between metals in the water and sediment and biota. Therefore it was concluded that the metals in the selected biota samples did not reflect the metals in the environment. The essential metals Cu, Zn and Cr were found to decrease at the end of the dry season and then increase at the end of the rainy season. The seasonal variations of metals in the river and biota maybe a result of the change of temperature in the area and the need for essential metals in the reproduction of fish. The results of this study clearly demonstrates that water spinach, snake head fish and swamp eel are not potential bio-indicators for metals in the Saigon River since they did not reflect concentrations of metals in their environment. It was also concluded based on consumption rates that water spinach, snake headfish and eel from the Saigon River do not present any potential health risk to consumers. However, attention should be paid to controlling the load of pollutants entering the river to avoid such risks and future problems.