A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization

Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the 'iron hypothesis'. For this reason, it is important to understand the response of pelagic biota to increased iron supply. Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest. Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days. This drawdown was mostly due to the proliferation of diatom stocks. But downward export of biogenic carbon was not increased. Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters. Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction.     

Reduced North Atlantic Deep Water flux to the glacial Southern Ocean inferred from neodymium isotope ratios

The global circulation of the oceans and the atmosphere transports heat around the Earth. Broecker and Denton suggested that changes in the global ocean circulation might have triggered or enhanced the glacial-interglacial cycles. But proxy data for past circulation taken from sediment cores in the South Atlantic Ocean have yielded conflicting interpretations of ocean circulation in glacial times--delta13C variations in benthic foraminifera support the idea of a glacial weakening or shutdown of North Atlantic Deep Water production, whereas other proxies, such as Cd/Ca, Ba/Ca and 231Pa/230Th ratios, show little change from the Last Glacial Maximum to the Holocene epoch. Here we report neodymium isotope ratios from the dispersed Fe-Mn oxide component of two southeast Atlantic sediment cores. Both cores show variations that tend towards North Atlantic signatures during the warm marine isotope stages 1 and 3, whereas for the full glacial stages 2 and 4 they are closer to Pacific Ocean signatures. We conclude that the export of North Atlantic Deep Water to the Southern Ocean has resembled present-day conditions during the warm climate intervals, but was reduced during the cold stages. An increase in biological productivity may explain the various proxy data during the times of reduced North Atlantic Deep Water export.     

Effect of natural iron fertilization on carbon sequestration in the Southern Ocean

The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean. Iron thus plays an important role in the carbon cycle, and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial-interglacial cycles. To date, the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments. It is difficult, however, to reliably assess the magnitude of carbon export to the ocean interior using such methods, and the short observational periods preclude extrapolation of the results to longer timescales. Here we report observations of a phytoplankton bloom induced by natural iron fertilization--an approach that offers the opportunity to overcome some of the limitations of short-term experiments. We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below. The efficiency of fertilization, defined as the ratio of the carbon export to the amount of iron supplied, was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments. This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration, suggesting that changes in iron supply from below--as invoked in some palaeoclimatic and future climate change scenarios--may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought.     

Mortality of sea lions along the central California coast linked to a toxic diatom bloom

Over 400 California sea lions (Zalophus californianus) died and many others displayed signs of neurological dysfunction along the central California coast during May and June 1998. A bloom of Pseudo-nitzschia australis (diatom) was observed in the Monterey Bay region during the same period. This bloom was associated with production of domoic acid (DA), a neurotoxin that was also detected in planktivorous fish, including the northern anchovy (Engraulis mordax), and in sea lion body fluids. These and other concurrent observations demonstrate the trophic transfer of DA resulting in marine mammal mortality. In contrast to fish, blue mussels (Mytilus edulus) collected during the DA outbreak contained no DA or only trace amounts. Such findings reveal that monitoring of mussel toxicity alone does not necessarily provide adequate warning of DA entering the food web at levels sufficient to harm marine wildlife and perhaps humans.     

Biochemistry: a cadmium enzyme from a marine diatom

The ocean biota contains a vast reservoir of genomic diversity. Here we present the sequence and preliminary characterization of a protein that is a cadmium-containing carbonic anhydrase from the marine diatom Thalassiosira weissflogii. The existence of a cadmium enzyme in marine phytoplankton may indicate that there is a unique selection pressure for metalloenzymes in the marine environment, and our discovery provides a long-awaited explanation for the nutrient-like behaviour of cadmium in the oceans.     

High mixing rates in the abyssal Southern Ocean

Mixing of water masses from the deep ocean to the layers above can be estimated from considerations of continuity in the global ocean overturning circulation. But averaged over ocean basins, diffusivity has been observed to be too small to account for the global upward flux of water, and high mixing intensities have only been found in the restricted areas close to sills and narrow gaps. Here we present observations from the Scotia Sea, a deep ocean basin between the Antarctic peninsula and the tip of South America, showing a high intensity of mixing that is unprecedented over such a large area. Using a budget calculation over the whole basin, we find a diffusivity of (39 plus minus 10) x 104[?]m2[?]s-1, averaged over an area of 7 x 105[?]km2. The Scotia Sea is a basin with a rough topography, situated just east of the Drake passage where the strong flow of the Antarctic Circumpolar Current is constricted in width. The high basin-wide mixing intensity in this area of the Southern Ocean may help resolve the question of where the abyssal water masses are mixed towards the surface.     

Riverine export of aged terrestrial organic matter to the North Atlantic Ocean

Global riverine discharge of organic matter represents a substantial source of terrestrial dissolved and particulate organic carbon to the oceans. This input from rivers is, by itself, more than large enough to account for the apparent steady-state replacement times of 4,00-6,000 yr for oceanic dissolved organic carbon. But paradoxically, terrestrial organic matter, derived from land plants, is not detected in seawater and sediments in quantities that correspond to its inputs. Here we present natural 14C and 13C data from four rivers that discharge to the western North Atlantic Ocean and find that these rivers are sources of old (14C-depleted) and young (14C-enriched) terrestrial dissolved organic carbon, and of predominantly old terrestrial particulate organic carbon. These findings contrast with limited earlier data that suggested terrestrial organic matter transported by rivers might be generally enriched in 14C from nuclear testing, and hence newly produced. We also find that much of the young dissolved organic carbon can be selectively degraded over the residence times of river and coastal waters, leaving an even older and more refractory component for oceanic export. Thus, pre-ageing and degradation may alter significantly the structure, distributions and quantities of terrestrial organic matter before its delivery to the oceans.     

Southern Ocean dust-climate coupling over the past four million years

Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean. Indeed, dust supply to the Southern Ocean increases during ice ages, and 'iron fertilization' of the subantarctic zone may have contributed up to 40?parts per million by volume (p.p.m.v.) of the decrease (80-100 p.p.m.v.) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles. So far, however, the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear. Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years, derived from the analysis of marine sediments from ODP Site 1090, located in the Atlantic sector of the subantarctic zone. The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years (refs 8, 9) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean, validating previous interpretations of the ice core data. The extension of the record beyond the interval covered by the Antarctic ice cores reveals that, in contrast to the relatively gradual intensification of glacial cycles over the past three million years, Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago. This finding complements previous observations over late Pleistocene glacial cycles, providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history.     

Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula

The disintegration of ice shelves, reduced sea-ice and glacier extent, and shifting ecological zones observed around Antarctica highlight the impact of recent atmospheric and oceanic warming on the cryosphere. Observations and models suggest that oceanic and atmospheric temperature variations at Antarctica's margins affect global cryosphere stability, ocean circulation, sea levels and carbon cycling. In particular, recent climate changes on the Antarctic Peninsula have been dramatic, yet the Holocene climate variability of this region is largely unknown, limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms. Here we show that surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 °C over the past 12,000 years, tracking the Holocene decline of local (65° S) spring insolation. Our results, based on TEX(86) sea surface temperature (SST) proxy evidence from a marine sediment core, indicate the importance of regional summer duration as a driver of Antarctic seasonal sea-ice fluctuations. On millennial timescales, abrupt SST fluctuations of 2-4 °C coincide with globally recognized climate variability. Similarities between our SSTs, Southern Hemisphere westerly wind reconstructions and El Ni?o/Southern Oscillation variability indicate that present climate teleconnections between the tropical Pacific Ocean and the western Antarctic Peninsula strengthened late in the Holocene epoch. We conclude that during the Holocene, Southern Ocean temperatures at the western Antarctic Peninsula margin were tied to changes in the position of the westerlies, which have a critical role in global carbon cycling.     

Efficient export of carbon to the deep ocean through dissolved organic matter

Oceanic dissolved organic carbon (DOC) constitutes one of the largest pools of reduced carbon in the biosphere. Estimated DOC export from the surface ocean represents 20% of total organic carbon flux to the deep ocean, which constitutes a primary control on atmospheric carbon dioxide levels. DOC is the carbon component of dissolved organic matter (DOM) and an accurate quantification of DOM pools, fluxes and their controls is therefore critical to understanding oceanic carbon cycling. DOC export is directly coupled with dissolved organic nitrogen and phosphorus export. However, the C:N:P stoichiometry (by atoms) of DOM dynamics is poorly understood. Here we study the stoichiometry of the DOM pool and of DOM decomposition in continental shelf, continental slope and central ocean gyre environments. We find that DOM is remineralized and produced with a C:N:P stoichiometry of 199:20:1 that is substantially lower than for bulk pools (typically >775:54:1), but greater than for particulate organic matter (106:16:1--the Redfield ratio). Thus for a given mass of new N and P introduced into surface water, more DOC can be exported than would occur at the Redfield ratio. This may contribute to the excess respiration estimated to occur in the interior ocean. Our results place an explicit constraint on global carbon export and elemental balance via advective pathways.     

Late Holocene paleoenvironmental changes in the southern Okinawa Trough inferred from a diatom record

We analyzed sediment diatoms from core MD05-2908 to infer climate and paleoenvironmental changes in the southern Okinawa Trough (SOT) over the past 1000 years.Because the study area is located in the East Asia monsoon area and beneath the main axis of Kuroshio Current,the climatic and hydrographical conditions are strongly influenced by both of these factors.The species used as environmental indicators,including the Kuroshio Current species (KC species) and freshwater species,were investigated in this paper.Changes in the abundance of the two groups of species revealed significant variations in water temperature and hydrography in the SOT during the Medieval Warm Period (MWP) and the Little Ice Age (LIA).From 950-1500 AD,the abundance of the KC species increased fluctuantly,while the freshwater species decreased,showing that the influence of the Kuroshio Current was intensified at that interval and the precipitation of the study area was relatively low.The KC species decreased remarkably and was maintained at a low abundance during the interval of 1500-1900 AD,which suggests that the impact of the Kuroshio Current on the SOT weakened during the period corresponding to the LIA.Moreover,the high abundance of the freshwater species at the same interval indicates a distinct increase in precipitation in northeastern Taiwan,which may be correlated to the south-detention of the rainfall belt in China caused by the southward migration of the western Pacific subtropical high.     

Unicellular C4 photosynthesis in a marine diatom

Nearly 50 years ago, inorganic carbon was shown to be fixed in microalgae as the C3 compound phosphoglyceric acid. The enzyme responsible for C3 carbon fixation, ribulose-1,5-bisphosphate carboxylase (Rubisco), however, requires inorganic carbon in the form of CO2 (ref. 2), and Rubisco enzymes from diatoms have half-saturation constants for CO2 of 30-60 microM (ref. 3). As a result, diatoms growing in seawater that contains about 10 microM CO2 may be CO2 limited. Kinetic and growth studies have shown that diatoms can avoid CO2 limitation, but the biochemistry of the underlying mechanisms remains unknown. Here we present evidence that C4 photosynthesis supports carbon assimilation in the marine diatom Thalassiosira weissflogii, thus providing a biochemical explanation for CO2-insensitive photosynthesis in marine diatoms. If C4 photosynthesis is common among marine diatoms, it may account for a significant portion of carbon fixation and export in the ocean, and would explain the greater enrichment of 13C in diatoms compared with other classes of phytoplankton. Unicellular C4 carbon assimilation may have predated the appearance of multicellular C4 plants.     

电厂粉煤灰炭制造活性炭的研究

以电厂粉煤灰炭为基础原料制造活性炭 ,实验结果表明 :原料经浮选后 ,只要原料中灰分小于1 5 % ,就可以制出性能较好的活性炭 实验采用煤焦油、沥青作为粘结剂 ,水蒸气为活化介质 ;同时 ,对生产过程主要影响因素进行了研究 活性炭的强度达 87% ,水容量为 1 0 1 .9% ,吸碘值 72 5mg/g ,亚甲基兰吸附值 1 39mg/g ,比表面积 1 0 35m2 /g 可用于有机溶的回收、空气与水的净化及作催化剂载体 ,产品质量高 ,经济效益及环境效益较好 图 1 ,表 6 ,参 5     

一株来源于深海热液区嗜热细菌的分离及鉴定

从西南印度洋热液区沉积物样品中分离纯化获得一株中度嗜热产芽孢杆菌,命名为M6.菌株M6为革兰氏阳性菌,短杆状,可成对.菌株M6的生长温度为35～65 ℃(最适生长温度60 ℃),生长pH为6.5～8.5(最适生长pH为7.0～8.0),生长NaCl质量分数为0～4%(最适NaCl质量分数为2%),生长盐度为0～80人工海水(最适盐度为40).16S rRNA基因相似性分析表明,菌株M6属于不产氧芽孢杆菌属(Anoxybacillus),与Anoxybacillus rupiensis菌株同源性最高,达99%;但16S～23S rDNA 间隔区PCR扩增分析表明,该菌与同属菌株有较大差异.通过以上形态学、生理特征以及分子生物学鉴定,认为菌株M6为不产氧芽孢杆菌属的菌株.另外,菌株M6可分泌胞外高温淀粉酶.菌株M6胞内含有内生质粒,其大小约为10 kb,命名为pAB01.     

Geological record and reconstruction of the late Pliocene impact of the Eltanin asteroid in the Southern Ocean

In 1995, an expedition on board the research vessel FS Polarstern explored the impact site of the Eltanin asteroid in the Southern Ocean, the only known asteroid impact into a deep ocean basin. Analyses of the geological record of the impact region place the event in the late Pliocene (approximately 2.15 Myr) and constrain the size of the asteroid to be >1 km. The explosive force inferred for this event places it at the threshold of impacts believed to have global consequences, and its study should therefore provide a baseline for the reconstruction and modelling of similar events, which are common on geological timescales.