Mesoscale phenomena are ubiquitous and highly energetic features of ocean circulation. Their influence on biological and biogeochemical processes varies widely, stemming not only from advective ...transport but also from the generation of variations in the environment that affect biological and chemical rates. The ephemeral nature of mesoscale features in the ocean makes it difficult to elucidate the attendant mechanisms of physical-biological-biogeochemical interaction, necessitating the use of multidisciplinary approaches involving in situ observations, remote sensing, and modeling. All three aspects are woven through this review in an attempt to synthesize current understanding of the topic, with particular emphasis on novel developments in recent years.
Mesoscale eddies, energetic vortices covering nearly a third of the ocean surface at any one time, modulate the spatial and temporal evolution of the mixed layer. We present a global analysis of ...concurrent satellite observations of mesoscale eddies with hydrographic profiles by autonomous Argo floats, revealing rich geographic and seasonal variability in the influence of eddies on mixed layer depth. Anticyclones deepen the mixed layer depth, whereas cyclones thin it, with the magnitude of these eddy‐induced mixed layer depth anomalies being largest in winter. Eddy‐centric composite averages reveal that the largest anomalies occur at the eddy center and decrease with distance from the center. Furthermore, the extent to which eddies modulate mixed layer depth is linearly related to the sea surface height amplitude of the eddies. Finally, large eddy‐mediated mixed layer depth anomalies are more common in anticyclones when compared to cyclones. We present candidate mechanisms for this observed asymmetry.
Plain Language Summary
Mesoscale eddies, rotating bodies of water that can be hundreds of kilometers across and reach thousands of meters into the ocean interior, are found nearly everywhere in the ocean. These eddies are know to transport vast amounts of heat, salt, and ocean life across hundreds to thousands of kilometers. This study investigates how these eddies control the depth to which the surface of the ocean is mixed. Wind and the transfer of heat between the ocean and atmosphere are two of the primary ways in which the ocean surface is homogenized. The depth of this mixed layer, the mixed layer depth, is shown to be deeper in eddies that are warm, when compared to their surrounds, and shallower in cold eddies. We show that the stronger or more energetic the eddies are, the larger their influence is on mixed layer depth.
Key Points
Anticyclonic and cyclonic eddies are observed to deepen and shoal the mixed layer, respectively
The largest eddy‐induced MLD anomalies are observed during the winter in regions of large eddy amplitude
Observations reveal that larger MLD anomalies are more common in anticyclones versus cyclones
Episodic eddy-driven upwelling may supply a significant fraction of the nutrients required to sustain primary productivity of the subtropical ocean. New observations in the northwest Atlantic reveal ...that, although plankton blooms occur in both cyclones and mode-water eddies, the biological responses differ. Mode-water eddies can generate extraordinary diatom biomass and primary production at depth, relative to the time series near Bermuda. These blooms are sustained by eddy/wind interactions, which amplify the eddy-induced upwelling. In contrast, eddy/wind interactions dampen eddy-induced upwelling in cyclones. Carbon export inferred from oxygen anomalies in eddy cores is one to three times as much as annual new production for the region.
Estimates of the ocean biological carbon pump are limited by uncertainties in the magnitude of the physical injection of particulate and dissolved organic carbon to the ocean interior. A major ...challenge is to evaluate the contribution of these physical pumps at small spatial and temporal scales (<100 km and <1 month). Here, we use a submesoscale permitting biophysical model covering a large domain representative of a subpolar and a subtropical gyre to quantify the impact of small‐scale physical carbon pumps.The model successfully simulates intense eddy‐driven subduction hot spots with a magnitude comparable to what has been observed in nature (1,000–6,000 mg C·m−2·day−1). These eddy‐driven subduction events are able to transfer carbon below the mixed‐layer, down to 500‐ to 1,000‐m depth. However, they contribute <5% to the annual flux at the scale of the basin, due to strong compensation between upward and downward fluxes. The model also simulates hot spots of export associated with small‐scale heterogeneity of the mixed layer, which intermittently export large amounts of suspended particulate and dissolved organic carbon. The mixed‐layer pump contributes ∼20% to the annual flux. High‐resolution measurements of export flux are needed to test models such as this one and to improve our mechanistic understanding of the biological pump and how it will respond to climate change.
Key Points
A high‐resolution model simulates realistic hot spots of organic carbon export by physical subduction
Eddy‐driven subduction contributes little to annual export due to compensation between upward and downward fluxes
Eddy‐driven spatiotemporal variations in the mixed‐layer efficiently export dissolved and particulate organic carbon
Mesoscale intrathermocline lenses are observed throughout the World Ocean and are commonly attributed to water mass anomalies advected from a distant origin. An alternative mechanism of local ...generation is offered herein, in which eddy-wind interaction can create lens-shaped disturbances in the thermocline. Numerical simulations illustrate how eddy-wind-driven upwelling in anticyclones can yield a convex lens reminiscent of a mode water eddy, whereas eddy-wind-driven downwelling in cyclones produces a concave lens that thins the mode water layer (a cyclonic "thinny"). Such transformations should be observable with long-term time series in the interiors of mesoscale eddies.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Marine animals, such as turtles, seabirds and pelagic fishes, are observed to travel and congregate around eddies in the open ocean. Mesoscale eddies, large swirling ocean vortices with radius scales ...of approximately 50-100 km, provide environmental variability that can structure these populations. In this study, we investigate the use of mesoscale eddies by 24 individual juvenile loggerhead sea turtles (Caretta caretta) in the Brazil-Malvinas Confluence region. The influence of eddies on turtles is assessed by collocating the turtle trajectories to the tracks of mesoscale eddies identified in maps of sea level anomaly. Juvenile loggerhead sea turtles are significantly more likely to be located in the interiors of anticyclones in this region. The distribution of surface drifters in eddy interiors reveals no significant association with the interiors of cyclones or anticyclones, suggesting higher prevalence of turtles in anticyclones is a result of their behavior. In the southern portion of the Brazil-Malvinas Confluence region, turtle swimming speed is significantly slower in the interiors of anticyclones, when compared to the periphery, suggesting that these turtles are possibly feeding on prey items associated with anomalously low near-surface chlorophyll concentrations observed in those features.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Atmospheric forcing, which is known to have a strong influence on surface ocean dynamics and production, is typically not considred in studies of the deep sea. Our observations and models demonstrate ...an unexpected influence of surface-generated mesoscale eddies in the transport of hydrothermal vent efflux and of vent larvae away from the northern East Pacific Rise. Transport by these deep-reaching eddies provides a mechanism for spreading the hydrothermal chemical and heat flux into the deep-ocean interior and for dispersing propagules hundreds of kilometers between isolated and ephemeral communities. Because the eddies interacting with the East Pacific Rise are formed seasonally and are sensitive to phenomena such as El Niño, they have the potential to introduce seasonal to interannual atmospheric variations into the deep sea.
Parasitic dinoflagellates of the genus Amoebophrya infect free-living dinoflagellates, some of which can cause harmful algal blooms (HABs). High prevalence of Amoebophrya spp. has been linked to the ...decline of some HABs in marine systems. The objective of this study was to evaluate the impact of Amoebophrya spp. on the dynamics of dinoflagellate blooms in Salt Pond (MA, USA), particularly the harmful species Alexandrium fundyense. The abundance of Amoebophrya life stages was estimated 3-7 days per week through the full duration of an annual A. fundyense bloom using fluorescence in situ hybridization coupled with tyramide signal amplification (FISH-TSA). More than 20 potential hosts were recorded including Dinophysis spp., Protoperidinium spp. and Gonyaulax spp., but the only dinoflagellate cells infected by Amoebophrya spp. during the sampling period were A. fundyense. Maximum A. fundyense concentration co-occurred with an increase of infected hosts, followed by a massive release of Amoebophrya dinospores in the water column. On average, Amoebophrya spp. infected and killed ∼30% of the A. fundyense population per day in the end phase of the bloom. The decline of the host A. fundyense population coincided with a dramatic life-cycle transition from vegetative division to sexual fusion. This transition occurred after maximum infected host concentrations and before peak infection percentages were observed, suggesting that most A. fundyense escaped parasite infection through sexual fusion. The results of this work highlight the importance of high frequency sampling of both parasite and host populations to accurately assess the impact of parasites on natural plankton assemblages.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
•Two source regions of pelagic Sargassum in the Gulf of Mexico (GoM) are revealed.•GoM Sargassum can originate from either the GoM interior or the Caribbean Sea.•The Loop Current System and eddies ...strongly impact Sargassum distributions.•Sargassum around Florida lags those near the Yucatan by about one month.
Pelagic Sargassum in the Gulf of Mexico (GoM) plays an important role in ocean biology and ecology, yet our knowledge of its origins and transport pathways is limited. Here, using satellite observations of Sargassum areal density and ocean surface currents between 2000 and 2023, we show that large amounts of Sargassum in the GoM can either originate from the northwestern GoM or be a result of physical transport from the northwestern Caribbean Sea, both with specific transport pathways. Sargassum of the northwestern GoM can be transported to the eastern GoM by ocean currents and eddies, eventually entering the Sargasso Sea. Sargassum entering the GoM from the northwestern Caribbean Sea can be transported in three different directions, with the northward and eastward transports governed by the Loop Current System (LCS) and westward transport driven by the westward extension of the LCS, the propagation or relaying of ocean eddies, the wind-driven westward currents on the Campeche Bank with or without eddies, and the westward currents with/without currents associated with eddies in the northern/central GoM. Overall, the spatial distribution patterns of pelagic Sargassum in the GoM are strongly influenced by the LCS and relevant eddies.
Using satellite observations of Sargassum areal density and ocean surface currents between 2000 and 2023, we show that large amounts of Sargassum in the Gulf of Mexico (GoM) can either originate from the northwestern GoM or be a result of physical transport from the northwestern Caribbean Sea, both with specific transport pathways. Sargassum of the northwestern GoM can be transported to the eastern GoM by ocean currents and eddies, eventually entering the Sargasso Sea. Sargassum entering the GoM from the northwestern Caribbean Sea can be transported in three different directions governed by the Loop Current System (LCS) and by ocean eddies and currents. Overall, the spatial distribution patterns of pelagic Sargassum in the GoM are strongly influenced by the LCS and relevant eddies, and Sargassum along the southeast coast of Florida lags that of the northwestern Caribbean Sea by about one month in most major Sargassum years. Display omitted
The coastal ocean comprises the semi-enclosed seas on the continental shelf, including estuaries and extending to the shelf break. This region is the focus of many serious concerns, including coastal ...inundation by tides, storm surges or sea level change; fisheries and aquaculture management; water quality; harmful algal blooms; planning of facilities (such as power stations); port development and maintenance; and oil spills. This book addresses modeling and simulation of the transport, evolution and fate of particles (physical and biological) in the coastal ocean. It is the first to summarize the state of the art in this field and direct it toward diverse applications, for example in measuring and monitoring sediment motion, oil spills and larval ecology. This is an invaluable textbook and reference work for advanced students and researchers in oceanography, geophysical fluid dynamics, marine and civil engineering, computational science and environmental science.
PDF
