Search

Abstract: In this paper, the multi-decadal variations of the Multivariate ENSO Index (MEI) and the Pacific Decadal Oscillation (PDO) index were studied to determine their influence on tropical cyclones (TCs) using the empirical mode decomposition (EMD) method and Hilbert spectral analysis. The ENSO and PDO are closely associated with various oceanic and atmospheric factors that govern TC activities in the western North Pacific (WNP). From the analysis results, multi-decadal oscillations with characteristic periods of 13 and 32.5years from MEI, and about 16.7 and 32.8years from PDO, were obtained. These values showed good agreement with the values obtained in other studies. The results of category 4–5 TCs and category 5 TCs also showed possible multi-decadal oscillations of about 15- and 37-year timescales, indicating that low frequency multi-decadal oscillations of intense TC occurrence in the WNP is influenced by the multi-decadal oscillations of ENSO and PDO. When seeking adaptation and mitigation measures for future climate scenarios, the multi-decadal variations of climate and their impacts on extreme events such as TCs should be taken into account together with the background of the global warming trend. [Copyright &y& Elsevier]

Abstract: Climate may affect marine fish populations through many different pathways, operating at a variety of temporal and spatial scales. Climate impacts may work their way bottom up through the food web or affect higher trophic levels more directly. In this review we try to disentangle and summarize some of the current knowledge made available through the rapidly increasing literature on the topic, with particular emphasis on the work within the Global Ocean Ecosystems Dynamics (GLOBEC) programme. We first consider different classification schemes and hypotheses relating climate through physical features of the ocean to population patterns. The response of a population or community to climate may be linear or non-linear, direct or indirect. The hypotheses may be classified according to the form of physical features in operation as being related to mixing, advection or temperature. The bulk of the paper is devoted to a region-by-region presentation and discussion of examples relating climate variability to marine fish populations. It is slanted towards the North Atlantic and North Pacific, but the tropical Pacific is also covered. By means of different categorization methods we compare climate responses between ecosystems. We conclude that the use of such classification schemes allows for a more precise description of the various ecosystems particular properties and facilitates inter-regional comparison. [Copyright &y& Elsevier]

Abstract: Understanding the role of the oceans in the Earth's changing climate requires comprehension of the relevant metabolic pathways which produce climatically important trace gases. The global ocean represents one of the largest natural sources of nitrous oxide (N2O) that is produced by selected archaea and/or bacteria during nitrogen (N) metabolism. In this study, the role of nitrite (NO2 −) in the production of N2O in the upper water column of the oligotrophic North Pacific Subtropical Gyre was investigated, focusing primarily on the lower euphotic zone where NO2 − concentrations at the primary NO2 − maximum reached 195nmolL−1. Free-drifting sediment trap arrays were deployed to measure N cycle processes in sinking particulate material and the addition of selected N substrates to unpreserved sediment traps provided an experimental framework to test hypotheses regarding N2O production pathways and controls. Sinking particles collected using NO2 −-amended, unpreserved sediment traps exhibited significant production of N2O at depths between 100 and 200m. Subsequent stable isotope tracer measurements conducted on sediment trap material amended with 15NO2 − yielded elevated δ15N values of N2O, supporting N2O production via a NO2 − metabolism pathway. Experiments on seawater collected from 150m showed N2O production via NO2 − metabolism also occurs in the water-column and indicated that the concentration of NO2 − relative to NH4 + availability may be an important control. These findings provide evidence for the production of N2O via nitrifer-denitrification in the lower euphotic zone of the open ocean, whereby NO2 − is reduced to N2O by ammonia-oxidizing microorganisms. [Copyright &y& Elsevier]

Abstract: Partial pressure of CO2 (pCO2) in surface seawater has been measured in the northeastern Pacific Ocean at Station P and along Line P since 1973. These data have been divided into ‘oceanic’ and ‘coastal/transition’ zones, and the seasonal and interannual variability and the long-term trends for each zone have been examined. The oceanic zone shows little seasonality in surface seawater pCO2, with undersaturation throughout the year. A strong, biologically-driven seasonal cycle is offset by variation in temperature-dependent solubility of CO2. The coastal/transition zone shows a decline in pCO2 from winter–spring through summer and fall that is likely the result of seasonal stratification and convection rather than coastal upwelling. Interannual variability all along Line P is correlated with the multivariate ENSO index (MEI), with lower seawater pCO2 associated with El Niño conditions. Correlations with the Pacific Decadal Oscillation Index are similar but weaker, in part because there are few data prior to the 1976 regime shift. The long-term trend in seawater pCO2 in the oceanic zone is +1.36±0.16μatmyear−1, indistinguishable from the atmospheric growth rate, and varies little among the seasons. In the coastal/transition zone a slow increase in the pCO2 of surface seawater relative to that of the atmosphere has led to increasing undersaturation, particularly in spring. Aliasing of the seasonal and interannual variability due to sampling frequency may explain part of the observed trend in the coastal/transition zone, but real changes in physical or biological processes are also possible and require more detailed study. [Copyright &y& Elsevier]

Abstract: As part of the research program Western Pacific Environment Study on CO2 Ocean Sequestration for Mitigation of Climate Change (WEST-COSMIC), plankton sampling was carried out down to great depths (maximum: 5800m) at four stations (44°N, 155°E; 39°N, 147°E; 30°N, 147°E and 25°N, 137°E) located in the western North Pacific Ocean. Ranges of plankton standing stock integrated over the water columns were wet mass (WM) 22–256gm-2, dry mass (DM) 1.3–27.4gm-2, carbon (C) 0.4–12.3gCm-2, nitrogen (N) 0.10–2.44gNm-2, ash (ash) 0.43–4.35gm-2, ash-free dry mass (AFDM) 0.9–21.8gm-2 and energy 20–582kJm-2. Log-linear equations were computed to allow interconversions among measurements in different mass units. Plankton mass was greater at higher latitudes. At each station, plankton mass decreased exponentially with increasing depth. This decrease was greater at subarctic (44°N) and subtropical (30°N and 25°N) stations than that at the transitional station (39°N) due to high amounts of diapausing copepods in meso- and bathypelagic depths at the latter station. Water content (% of WM), C:N ratios and ash (% of DM) increased with increasing depth, while C, N, AFDM (% of DM) and energy contents (Jmg-1 DM) showed an opposite pattern. Extremely low C (24–25% of DM), N (3.2–4.4% of DM), AFDM (48–56% of DM) and energy contents (10–12Jmg-1 DM), accompanied by high C:N ratios (5.7–8.0 by weight), of plankton samples from depths below 3000m suggest possible dominance of detritus in samples from that layer. The overall effect of detritus in measuring chemical composition of plankton samples is discussed. [Copyright &y& Elsevier]