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Iskhaq Iskandar Hideharu Sasaki Yoshikazu Sasai Yukio Masumoto Keisuke Mizuno 《Ocean Dynamics》2010,60(3):731-742
An eddy-resolving coupled physical–biological model is used to study the effect of cyclonic eddy in enhancing offshore chlorophyll-a (Chl-a) bloom in the southeastern tropical Indian Ocean during boreal summer–fall 2006. The results demonstrate that the offshore
Chl-a blooms are markedly coincident with the high eddy kinetic energy. Moreover, the vertical variations in Chl-a, nitrate, temperature, and mixed-layer depth (MLD) strongly imply that the cyclonic eddies induce surface Chl-a bloom through the injection of nutrient-rich water into the upper layer. Interestingly, we found that the surface bloom only
occurs when the deep Chl-a maximum is located within the MLD. On the other hand, the response of subsurface Chl-a to the eddy pumping is remarkable, although it is hardly observable at the surface. 相似文献
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We review the methodologies used to quantify climate feedbacks in coupled models. The method of radiative kernels is outlined and used to illustrate the dependence of lapse rate, water vapor, surface albedo, and cloud feedbacks on (1) the length of the time average used to define two projected climate states and (2) the time separation between the two climate states. Except for the shortwave component of water vapor feedback, all feedback processes exhibit significant high-frequency variations and intermodel variability of feedback strengths for sub-decadal time averages. It is also found that the uncertainty of lapse rate, water vapor, and cloud feedback decreases with the increase in the time separation. The results suggest that one can substantially reduce the uncertainty of cloud and other feedbacks with the accumulation of accurate, long-term records of satellite observations; however, several decades may be required. 相似文献
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Interannual modulation of mesoscale eddy activity at the intraseasonal timescale in the southeastern tropical Indian Ocean
and its relation to the Indian Ocean dipole mode (IOD) events are investigated using results from a high-resolution ocean
general circulation model. The model reproduces observed characteristics of the intraseasonal variability and its interannual
modulation fairly well, with large variances of the intraseasonal variability during the 1994 and 1997/1998 IOD events. Large
negative temperature anomaly off the coasts of Java and the Lesser Sunda Islands in boreal summer, due to seasonal variation
and interannual anomaly, extended further to the east in 1994, and the associated strong Indonesian throughflow enhanced the
baroclinic instability in the upper layer, generating anomalously large mesoscale eddy activity. The eddy heat transport,
in turn, significantly affected decaying phase of the 1994 IOD event. On the other hand, the development of the cold region
off the Java Island associated with the 1997/1998 IOD event occurred in boreal winter, causing weaker baroclinic instability
and hence weaker eddy activity off Java. This led to little influence on the heat budget in the southeastern tropical Indian
Ocean for the 1997/1998 IOD event. 相似文献
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An international demonstration (RD&D) project for ocean storage of radioactive wastes should be proposed, to study the feasibility of the concept of ocean storage of nuclear waste. This international project should utilize the scientific, engineering and technical capabilities of selected universities, oceanographic institutions, NGOs and industries. This project would need to be an independent (non-governmental) study, utilizing the capabilities of selected universities, oceanographic institutions, environmental NGOs (Non-Governmental Organizations) and industries. Scientists and engineers first need to conduct an engineering, environmental, and economic feasibility study of the concept. The goal of the project would be to determine if ocean-based storage reduced the risks to the environment and public health to a greater degree than land-based storage. This would require comparing the risks and factors involved and making the data and information available to anyone, anywhere, anytime on the internet. The mere presence of an investigation of the ocean storage option could facilitate scientific and engineering competition between the two options, could subsequently reduce environmental and public risks and provide better protection and cost benefits in the system utilized. One of the primary concerns of the scientific community would be related to the sensitivity and precision of the monitoring of individaul containers on the ocean bottom. An advantage of the land-based option is that if there is a release, its presence could be detected at very low levels and be contained in the storage facility. On the ocean bottom, a release from a container might not be easily detected due to dispersion. Therefore the containment system would have to be a system within a system with monitoring between the two providing greater protection. Ocean storage may have greater technical and political hurdles than land-based options, but it may provide greater protection over time, because it negates the threat of terrorism, it therefore merit further study. In the future if the use of nuclear energy and nuclear wastes increases, the global society could benefit from this international project, because it could reduce environmental and public health risks and promote energy independence. 相似文献
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We investigate the transient response of the global coupled ocean?Catmosphere system to enhanced freshwater forcing representative of melting of the Greenland ice sheets. A 50-year long simulation by a coupled atmosphere?Cocean general circulation model (CGCM) is compared with another of the same length in which Greenland melting is prescribed. To highlight the importance of coupled atmosphere?Cocean processes, the CGCM results are compared with those of two other experiments carried out with the oceanic general circulation model (OGCM). In one of these OGCM experiments, the prescribed surface fluxes of heat, momentum and freshwater correspond to the unperturbed simulation by the CGCM; in the other experiment, Greenland melting is added to the freshwater flux. The responses by the CGCM and OGCM to the Greenland melting have similar patterns in the Atlantic, albeit the former having five times larger amplitudes in sea surface height anomalies. The CGCM shows likewise stronger variability in all state variables in all ocean basins because the impact of Greenland melting is quickly communicated to all ocean basins via atmospheric bridges. We conclude that the response of the global climate to Greenland ice melting is highly dependent on coupled atmosphere?Cocean processes. These lead to reduced latent heat flux into the atmosphere and an associated increase in net freshwater flux into the ocean, especially in the subpolar North Atlantic. The combined result is a stronger response of the coupled system to Greenland ice sheet melting. 相似文献
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The aim of this paper is to test the effectiveness of feature models in ocean acoustic forecasting. Feature models are simple mathematical representations of the horizontal and vertical structures of ocean features (such as fronts and eddies), and have been used primarily for assimilating new observations into forecasts and for compressing data. In this paper we describe the results of experiments in which the models have been tested in acoustic terms in eddy and frontal environments in the Iceland Faeroes region. Propagation-loss values were obtained with a 2D parabolic-equation (PE) model, for the observed fields, and compared to PE results from the corresponding feature models and horizontally uniform (range-independent) fields. The feature models were found to represent the smoothed observed propagation-loss field to within an rms error of 5 dB for the eddy and 7 dB for the front, compared to 10–15-dB rms errors obtained with the range-independent field. Some of the errors in the feature-model propagation loss were found to be due to high-amplitude oceanographic noise in the field. The main conclusion is that the feature models represent the main acoustic properties of the ocean but do not show the significant effects of small-scale internal waves and fine-structure. It is recommended that feature models be used in conjunction with stochastic models of the internal waves, to represent the complete environmental variability. 相似文献
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Greg Hofmeyr GJ Bester MN Kirkman SP Lydersen C Kovacs KM 《Marine pollution bulletin》2006,52(9):1077-1080
Entanglements of Antarctic fur seals Arctocephalus gazella were recorded during four summers from 1996 to 2002 at the subantarctic island, Bouvetøya. Rates of entanglement varied between 0.024% and 0.059%. These rates are low for a pinniped population and might be because of the geographic isolation of the haulout site. An apparent decrease in the levels of entanglement over the course of the study was likely due, at least in part, to the removal of entanglements by observers. At least two-thirds of entangling materials were generated by fishery sources. Since there is no known local source of anthropogenic marine pollution, seals become entangled either in waters distant from the island, or when materials drift into local waters. Significantly more subadults were found entangled than expected from the postulated population age class distribution. 相似文献
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Although the Arctic methane reservoir is large,the emission of methane from the Arctic Ocean into the atmosphere remains poorly constrained.Continuous ship-borne measurements of atmospheric methane near the surface ocean were carried out during two cruises to investigate methane emission from the Arctic Ocean up to the latitude of 87°N.Three-day air mass back trajectories along the cruise tracks indicated that the surface Arctic Ocean could be a potentially important source of methane to the atmosphere.Rapid bursts in methane concentration occurred mainly along the ocean frontal area,suggesting that frontal upwelling in the upper layer of the Arctic Ocean might contribute to methane emissions into the atmosphere. 相似文献
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《Journal of Atmospheric and Solar》2002,64(3):291-305
The Intensive Field Phase of Indian Ocean Experiment (INDOEX, IFP-99) was carried onboard Oceanic Research Vessel Sagar Kanya during January 20–March 12, 1999 over the latitudinal range 15°N–20°S and the longitudinal range 63°E–77°E. The present study deals with the spatial variation of air–sea fluxes over the Indian Ocean during the INDOEX, IFP-99 campaign. Drag coefficient (C_D), and sensible heat (CH) and water vapor (CE) exchange coefficients are determined using an iterative scheme. The estimated values of these coefficients are utilized for the computation of air–sea fluxes using the bulk aerodynamic method. The variations of air–sea flux estimates are studied with respect to the variation of wind speed. 相似文献
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A simple biogeochemical model coupled to an offline ocean tracer transport model driven by reanalysis ocean data is used to simulate the seasonal and interannual CO $_2$ flux variability in the northern Indian Ocean. The maximum of seasonal and interannual CO $_2$ emission variances in the northern Indian Ocean are located in the coastal Arabian Sea (AS) and Southern Peninsular India (SP) with a basin-wide seasonal amplitude and standard deviation of 0.044 $\pm $ 0.04 Pg C year $^{-1}$ . The area integrated CO $_2$ emissions from these two regions in the model are significantly correlated (above a 95 % level) with the observations of Takahashi et al. (Deep-Sea Res-II, 56:554–577, 2009). The interannual anomalies of CO $_2$ emission from the AS and SP are found as 40 and 30 % of their respective seasonal amplitudes. Both the Arabian Sea (AS) and Southern Peninsular India (SP) interannual CO $_2$ emission anomalies show a 3–4-year variability. The correlations of AS and SP CO $_2$ emission anomalies with the Indian Ocean Dipole/Zonal Mode (IODZM) and Southern Oscillation (SO) indices from 1980 to 1999 are 0.35, 0.21 and 0.32, 0.01 respectively. A 5-year window moving correlation analysis shows that the relationship of AS and SP CO $_2$ emission to the SO and IODZM are complementary to each other. During the years when the correlation of air–sea CO $_2$ emission with the IODZM is stronger, the corresponding correlation with the SO is weaker or opposite. The total change in pCO $_2$ is broken down into changes induced by the individual components such as dissolved inorganic carbon (DIC), sea surface temperature (SST), alkalinity, and salinity and found that (1) the effect of SST in the AS CO $_2$ emission increases (decreases) when the correlation of CO $_2$ emission with the IODZM is positive (negative), and (2) the SP CO $_2$ emission is strongly controlled by the circulation-driven DIC changes; however, this relation is found to be weaker when the SO correlates negatively with the SP CO $_2$ emission. 相似文献
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Tide gauge data collected from Sri Lanka (three stations) and Western Australia (eleven stations) during the Indian Ocean tsunamis, which occurred in December 2004, March 2005, July 2006, and September 2007, and incorporated five tsunamis, were examined to determine tsunami behaviour during these events. During the December 2004 tsunami, maximum wave heights of 3.87 m and 1.75 m were recorded at Colombo (Sri Lanka) and Bunbury (Western Australia), respectively. The results indicated that although the relative magnitudes of the tsunamis varied, the tsunami behaviour at each station was similar. This was due to the effect of the local and regional topography. At all tide gauges, the spectral energy corresponding to periods between 20 and 85 minutes increased during the tsunami. The sea-level data obtained from the west and south coasts of Sri Lanka (Colombo and Kirinda) indicated the importance of wave reflections from the Maldives Island chain, which produced the maximum wave two to three hours after the arrival of the first wave. In contrast, Trincomalee on the east coast did not show evidence of a reflected wave. Similarly, along the west coast of Australia, the highest waves occurred 15 hours after the arrival of the first wave. Here, based on travel times, we postulated that the waves were reflected from the Mascarene Ridge and/or the Island of Madagascar. Reflected waves were not present in the 2006 tsunami, where the primary waves propagated away from topographic features. One of the main influences of the tsunami was to set up oscillations at the local resonance frequency. Because Sri Lanka and Western Australia have relatively straight coastlines, these oscillations were related to the fundamental period of the shelf oscillation. For Colombo, this corresponded to 75-minute period, whereas in Geraldton and Busselton (Australia), the four-hour period was most prominent; at Jurien Bay and Fremantle, the resonance period was 2.7 hours. 相似文献