Satellite observation and model simulation of upper ocean biophysical response to Super Typhoon Nakri

In this paper, we use multi-satellite remote sensing data and Regional Ocean Model System (ROMS) to examine the physical and biological responses to Typhoon Nakri during a period from 1 to 8 June 2008 in the western North Pacific. From satellite observations, we find remarkable surface cooling (∼5 °C) and distinct phytoplankton enhancement after Nakri passage. It is interesting to note that in contrast to the well-documented rightward bias of the surface cooling response, the maximum biological response to Nakri occurred on the left of the Nakri’s track rather than the right side, where the most distinct cooling response occurred. To reveal the dynamic mechanism for this unusual phenomenon, we have done numerical experiments with and without the influence of preexisting cyclonic circulation and previous typhoon. The results from simulations show that both the physical and biological responses to Nakri are greatly affected by the preexisting cyclonic circulations. The discrepancy between the locations of maximum physical and biological responses mainly results from the advanced uplift and current advection of nutrient fields by previous typhoon Rammasun, which passed through the area about two weeks before Nakri.     

An eddifying Stommel model: fast eddy effects in a two-box ocean

ABSTRACT

A system of stochastic differential equations is formulated describing the heat and salt content of a two-box ocean. Variability in the heat and salt content and in the thermohaline circulation between the boxes is driven by fast Gaussian atmospheric forcing and by ocean-intrinsic, eddy-driven variability. The eddy forcing of the slow dynamics takes the form of a colored, non-Gaussian noise. The qualitative effects of this non-Gaussianity are investigated by comparing to two approximate models: one that includes only the mean eddy effects (the “averaged model”), and one that includes an additional Gaussian white-noise approximation of the eddy effects (the “Gaussian model”). Both of these approximate models are derived using the methods of fast averaging and homogenisation. In the parameter regime where the dynamics has a single stable equilibrium the averaged model has too little variability. The Gaussian model has accurate second-order statistics, but incorrect skew and rare-event probabilities. In the parameter regime where the dynamics has two stable equilibria the eddy noise is much smaller than the atmospheric noise. The averaged, Gaussian, and non-Gaussian models all have similar stationary distributions, but the jump rates between equilibria are too small for the averaged and Gaussian models.     

Estimate of eddy energy generation/dissipation rate in the world ocean from altimetry data

Assuming eddy kinetic energy is equally partitioned between the barotropic mode and the first baroclinic mode and using the weekly TOPEX/ERS merged data for the period of 1993~2007, the mean eddy kinetic energy and eddy available gravitational potential energy in the world oceans are estimated at 0.157 and 0.224 EJ; the annual mean generation/dissipation rate of eddy kinetic energy and available gravitational potential energy in the world oceans is estimated at 0.203 TW. Scaling and data analysis indicate that eddy available gravitational potential energy and its generation/dissipation rate are larger than those of eddy kinetic energy.     

Rapid dissipation of a Loop Current eddy due to interaction with a severe Gulf of Mexico hurricane

Ocean Dynamics - Loop Current Eddies (LCEs) are warm-core, anticyclonic rings that shed from the Loop Current and migrate westward providing kinetic and potential energy to the Gulf of...     

Linkage between multi-model uncertainties and the role of ocean heat content in ocean carbon uptake

Ocean heat content (OHC) plays an important role in ocean carbon uptake (OCU). However, the changes of OHC and OCU are model-dependent and have large bias compared with observations. This makes it difficult to quantify their relationship. Here, we propose a new metric to measure the uncertainty of the relationship between OHC and OCU. The new metric can link the uncertainty with different OCU processes and allow direct comparison of the impact of OHC on the OCU in different simulations. The metric is illustrated in different simulations of the Coupled Model Intercomparison Project phase 5 (CMIP5) in which atmospheric CO₂ is increased by 1%/year. Results show that OHC in 0–500 m plays a dominant role in the OCU for the radiatively coupled (RAD) experiment because warming intensifies the carbon loss in the upper ocean. Relatively, OHC in the intermediate waters (500–2000 m) are crucial for the fully coupled and biogeochemically coupled experiment because this layer largely regulates the OCU. For different ocean basins, the intermediate Southern Ocean and deep North Atlantic are more important for the OCU in the RAD simulation. The metric also suggests the importance of global overturning circulation and the Southern Ocean in the OCU.     

Mercury partition in the interface between a contaminated lagoon and the ocean: The role of particulate load and composition

After having estimated the patterns of flow to the ocean and found some seasonal and tidal differences, mainly with regard to the relative importance of dissolved and particulate fractions, mercury partitioning at the interface between a contaminated lagoon and the Atlantic Ocean was investigated during four tidal cycles in contrasting season and tidal regimes. Mercury was found to be located predominantely in the particulate fraction throughout the year, contributing to its retention within the system. Seasonal conditions, variations in marine and fluvial signals and processes affecting bed sediment resuspension influenced the character and concentration of suspended particulate matter in the water column. Variation in the nature, levels and partitioning of organic carbon in the particulate fraction affected levels of particulate mercury as well as mercury partitioning. These results highlight the dominant role of suspended particulate matter in the distribution of anthropogenic mercury and reinforce the importance of competitive behavior related to organic carbon in mercury scavenging.     

Observations on the flow structures and transport in a simulated warm-core ring in the Gulf of Mexico

This study presents several new observations from the study of a numerically simulated warm-core ring (WCR) in the Gulf of Mexico based on the ECCO2 global ocean simulation. Using Lagrangian coherent structures (LCS) techniques to investigate this flow reveals a pattern of transversely intersecting LCS in the mixed layer of the WCR which experiences consistent stretching behavior over a large region of space and time. A detailed analysis of this flow region leads to an analytical model of the velocity field which captures the essential elements that generate the transversely intersecting LCS. The model parameters are determined from the simulated WCR and the resulting LCS show excellent agreement with those observed in the WCR. The three-dimensional transport behavior that creates these structures relies on the small radial outflow that is present in the mixed layer and is not seen below the pycnocline, leading to a sharp change in the character of the LCS at the bottom of the mixed layer. The flow behavior revealed by the LCS limits fluid exchange between the WCR and the surrounding ocean, contributing to the long life of WCRs. Further study of these structures and their associated transport behavior may lead to further insights into the development and persistence of such geophysical vortices as well as their transport behavior.     

The overlooked role of the ocean in mercury cycling in the Arctic

The rapid and high bioaccumulation of mercury in marine mammals and its spatial and temporal variations have been a major puzzle in the Arctic. While extensive efforts have been focussed on the monitoring and chemistry of atmospheric mercury depletion events, a recent mass budget estimate of mercury in the Arctic suggests that we have overlooked the role of the ocean itself. Only through focussed studies on Hg dynamics in the Arctic Ocean under a changing climate are we going to understand what the risk of mercury is to those marine ecosystems and the people who rely on them.     

A new approach to the Nd residence time in the ocean: the role of atmospheric inputs

Concentrations of rare earth elements (REE) and Nd isotopic ratios were analyzed for seawater, filtered suspension and sediment trap samples collected in the tropical Atlantic Ocean (EUMELI program, EUtrophic, MEsotrophic and oLIgotrophic sites, 20°N, 18°–21°W). This is the first REE/Nd dataset on solution and different-sized particles collected at the same site. We present direct evidence of the Nd isotopic exchange between particulate lithogenic fraction and seawater without significant mass transfer. This exchange is probably one of the main factors that simultaneously constrains the Nd concentration and isotopic ratio budget. We propose a new approach to estimate the residence time of Nd in the ocean (τ_Nd) based on isotopic exchange: 200 yr < τ_Nd< 1000 yr. The exchange requires a partial dissolution of lithogenic Nd. We estimate that the fraction of soluble Nd proportion in atmospheric dust is of the order of 20% based on the isotopic ratios. We suggest that the partial dissolution of atmospheric fallout is probably one of the main REE sources of the ocean.     

Correction to: Observation of submesoscale turbulence in a cyclonic eddy

Ocean Dynamics - In this study, we report results from a high-resolution measurement of submesoscale turbulence in a mesoscale eddy. The kinetic energy spectra in the mesoscale eddy are decomposed...     

Increasingly important role of numerical modeling in oceanic observation design strategy: A review

Science China Earth Sciences - Oceanic observation design is of considerable significance and has made remarkable progress during the past several decades. This study addresses the critical role of...     

Melting temperatures of the Allende meteorite: implications for a Hadean magma ocean

Melting temperatures of the silicate fraction of the Allende CV3 meteorite, at upper mantle pressures, are several hundred degrees lower than that of fertile peridotite xenoliths or ‘pyrolite’. If the Earth accreted from material similar to chondrites, then deep mantle melting could have occurred with a relatively modest heat budget. It is concluded that initial chemical composition is an important variable in realistic magma ocean models.     

Turbulence structure in the upper ocean: a comparative study of observations and modeling

Observations of turbulent dissipation rates measured by two independent instruments are compared with numerical model runs to investigate the injection of turbulence generated by sea surface gravity waves. The near-surface observations are made by a moored autonomous instrument, fixed at approximately 8 m below the sea surface. The instrument is equipped with shear probes, a high-resolution pressure sensor, and an inertial motion package to measure time series of dissipation rate and nondirectional surface wave energy spectrum. A free-falling profiler is used additionally to collect vertical microstructure profiles in the upper ocean. For the model simulations, we use a one-dimensional mixed layer model based on a k–ε type second moment turbulence closure, which is modified to include the effects of wave breaking and Langmuir cells. The dissipation rates obtained using the modified k–ε model are elevated near the sea surface and in the upper water column, consistent with the measurements, mainly as a result of wave breaking at the surface, and energy drawn from wave field to the mean flow by Stokes drift. The agreement between observed and simulated turbulent quantities is fairly good, especially when the Stokes production is taken into account.     

A numerical study on the role of atmospheric forcing on mixed layer depth variability in the Bay of Bengal using a regional ocean model

Ocean Dynamics - This study investigates the role of driving atmospheric forces [winds, net heat flux, and evaporation–precipitation (E–P)] and the possible mechanisms on the mixed...     

Design and analysis of the Sydney deepwater ocean outfall environmental monitoring programme: a critique

The Sydney Environmental Monitoring Programme (EMP) measured the environmental performance of Sydney's new deepwater sewage outfalls against a wide range of criteria related to impacts on marine ecosystems and on human use of marine resources. It consisted of a number of interacting studies conducted during the period 1989 to 1993. Given that all the studies have now been finalized and the data analysed and presented (see papers in this volume), it is appropriate to review the program as a whole and identify, with the benefit of hindsight, where things could have been done better. This paper focuses mainly on the experimental design and statistical treatment of the studies conducted, although management problems are also briefly addressed. Overall it is concluded that the studies making up the EMP contributed greatly to enhancing our understanding of the marine environment of the coastal shelf off Sydney, an area which had previously received only limited attention. Most of the studies, however, suffered from deficiencies in experimental design, which was difficult to overcome when analysing the data. It will be important, in designing future integrated monitoring studies, to draw on the experience of programs such as this to avoid some of the pitfalls which appear to be inherent in these types of large programs.     

The photosynthetic oxygen evolution does not exclude the important role and contribution of bicarbonate photolysis

Photosynthesis is the most important biochemical reaction on Earth. It has co-evolved and developed with the Earth, driving the biogeochemical cycle of all elements on the planet and serving as the only chemical process in nature that can convert light energy into chemical energy. Some heavy oxygen isotopic(¹⁸O) labeling experiments have‘‘conclusively’’ demonstrated that the oxygen released by photosynthesis comes only from water and are written into textbooks. However, it is not diff...     

Mean and eddy motion in the Skagerrak/northern North Sea: insight from a numerical model

Insight regarding the mean and eddy motion in the Skagerrak/northern North Sea area is gained through an analysis of model-simulated currents, hydrography, kinetic energy and relative vorticity for the 2 years 2000 and 2001. In this a -coordinate ocean model is used. Since the tidal currents are generally strong in the area, care is exercised to distinguish the mesoscale (eddy) motion from higher-frequency motion such as tides, before computing the mean and eddy kinetic energy. The model-simulated response is first compared with available knowledge of the circulation in the area, and when available, also with sea-surface temperature obtained from satellite imagery. It is concluded that the model appears to faithfully reproduce most of what is known, in particularly the upper mixed layer circulation. An analysis of the mean and eddy kinetic energy reveals that many of the mesoscale structures found in the area are recurrent. This is particularly true for the structures off the southern tip of Norway. Also in general, areas of strong mean and eddy kinetic energy are co-located. The exception is the area off the southern tip of Norway, where the eddy kinetic energy is much larger than its mean counterpart. An analysis of the relative vorticity reveals that the variability found is due to the occurrence of recurrent anticyclonic eddies. It is hypothesized that these eddies are generated due to an offshore veering of the Norwegian coastal current (NCC) as it reaches the eastern end of the Norwegian Trench plateau. Here it becomes a free jet, which is then vulnerable to either barotropic instability caused by the horizontal shear in the jet-like structure of the NCC at this point, or a baroclinic (frontal) instability. The latter may come into play when the NCC veers offshore and its relatively fresh water meets the inflowing saline water of Atlantic origin, a frontogenesis that may become strong enough for cyclogenesis to take place. Due to the depth-independent nature of the model-generated eddies, the barotropic instability is the most likely candidate. It remains to resolve the reason for the offshore veering of the NCC. The most likely candidate mechanisms are vortex squeezing or simply that the coastline curvature is large enough for the NCC to separate from the coast in a hydraulic sense.Responsible Editor: Phil Dyke     

中美洲鹦鹉湾气旋涡的亚中尺度结构特征

海洋中普遍存在的涡旋对全球海洋热、盐通量有重要贡献.一条于2000 年6 月在中美洲鹦鹉湾采集的地震剖面L115 捕获到了一个海水次表层透镜状反射结构.透镜状反射的宽度约 150 km,厚度约500 m,深度从 100 m延伸到约600 m,核心深约200 m.结合和地震采集时间近同步的再分析数据中的流速和海水温度数据...