Abyssal Currents Research Articles

The first Mud Dragons (Kinorhyncha) from the Emperor Seamount Chain (Northwestern Pacific) with notes on their biogeography and distribution patterns in the Pacific Deep-Sea

Seamounts and oceanic currents play crucial roles in shaping the genetic diversity of species by either acting as barriers or pathways for species dispersal. In the meiofaunal samples collected using ROV facilities at the slope of the Koko Guyot (2172 m) in the southernmost part of the Emperor Seamount Chain in the Northwestern Pacific, we found representatives of three kinorhynch genera, Echinoderes cf. lupherorum Sørensen et al. 2018, Campyloderes cf. vanhoeffeni Zelinka, 1913 and Sphenoderes sp. 1., previously known from other locations in the Pacific. Kinorhynchs were studied and illustrated using light (LM) and scanning electron (SEM) microscopy to prove the species identity and to compare morphological variations with representatives of these species collected from other, very distant localities in the Pacific. We illustrate the pan-oceanic distribution of the collected species with a system of abyssal currents in the Pacific. The probable distribution pattern corresponds with the northward pathway of Antarctic Bottom Water out of the Southern Ocean in the Pacific through the deep-sea area off New Zealand. Echinoderes lupherorum appears to be the first representative of the Echinoderidae with the pan-Pacific distribution. Discussions on the biogeography of Campyloderes cf. vanhoeffeni Zelinka, 1913 and Sphenoderes in the Pacific are also provided.

Mesoscale eddy-strengthened deep-sea topographic Rossby waves in the southwestern South China Sea.

Topographic Rossby waves (TRWs) dominate the low-frequency variability of deep ocean currents and play a crucial role in energy exchange and material mixing. On the continental slope of the southwestern South China Sea, a deep-water mooring was deployed to observe TRWs for a period of ~ 40days. The TRWs, with a wavelength of 109km, account for 41.3% of the subinertial variations. A ray-tracing model was applied to investigate the propagation and energy source. The results showed that the TRWs propagated from the northeast of the mooring location and were most likely caused by the mesoscale eddy disturbances off the Vietnam coast. This study provides a new perspective on examining the impact of mesoscale eddies off Vietnam on abyssal currents.

Sea level anomalies affect the ocean circulation at abyssal depths

Abyssal channels are the key points controlling bottom circulation of the World Ocean. They provide meridional transport of the coldest Antarctic Bottom Water between deep-water basins influencing the meridional overturning circulation and the climate on a global scale. Here we show that the synoptic variability of deep-water flows including blocking abyssal currents between deep ocean basins is related to sea level anomalies observed over the channels. Our results demonstrate that processes at the ocean surface have a more significant connection with the bottom circulation than it was considered earlier. This study opens a discussion of the importance of mesoscale eddies and air-sea interactions on water exchange between abyssal basins, meridional heat transport in the ocean, and possible responses of the ocean to the observed sea level rise in a changing climate.

Intra-seasonal variability of the abyssal currents in COMRA’s contract area in the Clarion-Clipperton Zone

Intra-seasonal variability of the abyssal currents in COMRA’s contract area in the Clarion-Clipperton Zone

Antarctic Bottom Water Jets Flowing from the Vema Channel

Properties of the abyssal current of Antarctic Bottom Water (AABW) from the Vema Channel are studied based on temperature, salinity, and velocity profiler (CTD/LADCP) data. Previous studies over a period of almost 30 years revealed that very intense current of AABW exists in the Vema Channel. Later, it was found that this current consists of two branches. One branch spreads over the bottom of the channel; the other branch is elevated over the western wall of the channel. The deepest branch decays after it passes approximately 100 km while the upper one continues further to the North Atlantic and is the source of abyssal waters in the Canary and Cabo Verde basins of the North Atlantic. Data analysis suggested that the upper jet splits into two. One of these descends down a canyon at 24°30′ S, while the other (the third one) remains on the continental slope, and indications of its existence are also found at 24°00′ S. This research analyzes the existence and pathway of this third branch that can be traced up to latitude 24° S. Velocity measurements in 2022 allowed us to confirm the existence of this third branch.

Structure and Variability of Abyssal Current in Northern South China Sea Based on CPIES Observations

AbstractThe abyssal current is important for water renewal and energy conversion in the deep South China Sea (SCS), and it potentially contributes to the upper and middle circulations. A mooring array including 11 current and pressure‐recording inverted echo sounders was deployed in the northern SCS between July 2016 and April 2019 to observe large‐scale and long‐term abyssal currents. The yearly averaged current flows southwestward following the boundary with a maximum velocity of 2.25–2.52 cm/s. The spatial structure exhibits a weaker and wider current in the north, where topography is subdued, whereas the current enhances and narrows on the steep slopes. The southwestward current is strong in the summer and autumn but is insignificant in the winter and spring. In the autumn, the current is narrower and closer to the boundary than that in the summer, and a northeastward countercurrent is found ∼60 km away from the western boundary. The southwestward and northeastward currents constitute the cyclonic circulation. Drastic temporal variability is observed in the deep ocean. The abyssal current is dominated by semidiurnal tides, diurnal tides, and near‐inertial waves (NIWs) in the high‐frequency band. Bursts of NIWs are observed in the deep ocean after two typhoons, and the NIWs propagate southwestward at a velocity of 2.4 m/s. The low‐frequency band is dominated by a westward‐propagating 70‐day fluctuation following the characteristics of topographic Rossby waves.

Intraseasonal Abyssal Current Variability of Bottom-Trapped Topographic Rossby Waves in the Southwestern East Sea (Japan Sea)

Examining the deep-water exchange through the Ulleung Interplain Gap (UIG) between the Ulleung Basin (UB) and the Japan Basin in the East Sea (Sea of Japan) is critical for understanding the vigorous circulation and material cycles of the sea. The exchange features an asymmetric flow structure across the UIG: a broad and weak inflow (into the UB) in the western UIG, and a narrow and strong outflow (out of the UB) in the eastern UIG, with the latter closely associated with the Dokdo Abyssal Current (DAC), a long-term mean, strong abyssal current near Dokdo. In this study, the linear theory of bottom-trapped topographic Rossby waves (TRWs) is applied to explain the previously unexplored longer intraseasonal band (30–50 days) DAC variability by analyzing multi-year moored current-meter observations and HYCOM reanalysis data, as they are significantly correlated in the period band (though not at the shorter intraseasonal band of 5–25 day explored previously). Bottom-intensified DAC variability is characterized by TRW parameters with a vertical trapping scale of 1100–2100 m, a horizontal wavelength of 49–111 km, a propagating speed of 1.3–3.0 km day-1, and a propagating direction aligned with isobaths within a 2°–23° range (shallower water on the right). The departure angle between the energy-propagating direction of the waves and the isobath direction is estimated from the spectra of the along- and cross-slope abyssal currents and from the TRW theoretical dispersion relation for a given buoyancy frequency and bottom slope. These values are then compared to examine the significance of the bottom-trapped TRW dynamics, yielding a small (< 16°) difference. The results support the significance of bottom-trapped TRWs on the longer intraseasonal variability of abyssal currents near the steeply sloped eastern side of the UIG, and an asymmetric abyssal flow structure across the UIG in the southwestern East Sea.

Some aspects of the deep abyssal overflow between the middle and southern basins of the Caspian Sea

Abstract. The present study investigates the deep gravity current between the middle and southern Caspian Sea basins caused by the density difference of deep waters. Oceanographic data, a numerical model and a dynamic model are used to consider the structure of this Caspian Sea abyssal overflow. The CTD data are obtained from UNESCO, and the three-dimensional COHERENS ocean model results are used to study the abyssal currents in the southern basin of the Caspian Sea. The deep overflow is driven by the density difference, which is mainly owing to the temperature difference, between the middle and southern basins, especially in winter. Due to cold weather in the northern basin, water sinks at high latitudes and after filling the middle basin it overflows into the southern basin. As the current passes through the Absheron Strait (or sill), we use the analytic model of Falcini and Salusti (2015) for the overflow gravity current to estimate the changes in the vorticity and potential vorticity of the flow over the Absheron sill; the effects of entrainment and friction are also considered. Due to the importance of the overflow with respect to deep water ventilation, a simple dynamical model of the boundary currents based on the shape of the Absheron Strait is used to estimate typical mass transport and flushing time; the flushing time is found to be about 15 to 20 years for the southern basin of the Caspian Sea. This timescale is important for the region's ecosystem and with respect to the impacts of pollution due to oil exploration. In addition, by reviewing the drilled oil and gas wells in the Caspian Sea, the results show that the deep overflow moves over some of these wells. Thus, the deep flow could be an important factor influencing oil pollution in the deeper region of the southern Caspian Sea.

Meridional dynamics of grounded abyssal water masses on a sloping bottom in a mid-latitude -plane

Observations, numerical simulations and theoretical scaling arguments suggest that in mid-latitudes, away from the source regions and the equator, the meridional transport of abyssal water masses along a continental slope corresponds to planetary geostrophic flows that are gravity- or density-driven and topographically steered. We investigate these dynamics using a nonlinear reduced-gravity model that can describe grounded abyssal meridional flow over sloping topography that crosses the planetary vorticity gradient. Exact nonlinear steady and time-dependent solutions are obtained. The general steady theory is illustrated for a non-parallel equatorward flow that possesses a single along-slope grounding along the upslope flank of the current (complementing previous work). Four specific nonlinear time-dependent solutions are described. Two initial-value problems are solved exactly. The first initial configuration corresponds to an equatorward abyssal flow that has no cross-slope shear in the along-slope velocity and possesses a single grounding along the upslope flank of the current. The nonlinear time-dependent evolution of this initial current into a non-parallel shear flow is described. The second initial condition corresponds to an isolated radially symmetric grounded abyssal pool or dome. The nonlinear time-dependent evolution of this abyssal dome, which propagates equatorward with unsteady along- and cross-slope velocities while deforming into an elliptically shaped abyssal dome with $\unicode[STIX]{x1D6FD}$-induced diminishing height, is described. Finally, the nonlinear time-dependent boundary-value problem can be solved exactly in which the in-flow boundary condition on the poleward boundary of the mid-latitude domain corresponds to a time-dependent abyssal current with both an upslope and downslope grounding. Two specific time-dependent boundary conditions are examined. The first corresponds to a time-limited surge in the equatorward volume transport in the abyssal current along the poleward boundary. The second configuration corresponds to the nonlinear evolution of a finite-amplitude downslope plume or loop that forms in the abyssal current that is reminiscent of those seen in baroclinic instability simulations.

Observation of the abyssal western boundary current in the Philippine Sea

Mooring observations were conducted from July 16, 2011 to March 30, 2012 east of Mindanao, Philippines (127A degrees 2.8'E, 8A degrees 0.3'N) to observe the abyssal current at about 5 600 m deep and 500 m above the ocean bottom. Several features were revealed: 1) the observed abyssal current was highly variable with standard deviations of 57.3 mm/s and 34.0 mm/s, larger than the mean values of -31.9 and 16.6 mm/s for the zonal and meridional components, respectively; 2) low-frequency current longer than 6 days exhibited strong seasonal variation, flowing southeastward (mean flow direction of 119.0A degrees clockwise from north) before about October 1, 2011 and northwestward (mean flow direction of 60.5A degrees counter-clockwise from north) thereafter; 3) the high-frequency flow bands were dominated by tidal currents O-1, K-1, M-2, and S-2, and near-inertial currents, whose frequencies were higher than the local inertial frequency. The two diurnal tidal constituents were much stronger than the two semidiurnal ones. This study provides for the first time an observational insight into the abyssal western boundary current east of Mindanao based on long-term observations at one site. It is meaningful for further research into the deep and abyssal circulation over the whole Philippine Sea and the 3D structure of the western boundary current system in this region. More observational and high-resolution model studies are needed to examine the spatial structure and temporal variation of the abyssal current over a much larger space and longer period, their relation to the upper-layer circulation, and the underlying dynamics.

Cross-equatorial flow of grounded abyssal ocean currents

The cross-equatorial flow of grounded abyssal ocean currents in a differentially rotating meridional channel with parabolic bottom topography is examined. In particular, the dependence is determined of the cross-equatorial volume flux on the underlying flow parameters including the slope of the channel’s walls , the half-width of the channel , the half-width and height of the abyssal current and , respectively, the magnitude of the rotation vector , the Earth’s radius , and the reduced gravity . In addition, it is shown that the ratio between the width of the channel and the zonal wavelength of a narrow wave structure that is formed by the current in the equatorial region plays a crucial role in determining into which hemisphere the current flows after its interaction with the equator. It is found that some parameters (e.g. and ) do not have any significant effect on the zonal wavelength, while variations in other parameters (e.g. , , , and ) change the zonal wavelength and, consequently, can dramatically alter the qualitative trans-equatorial behavior of the abyssal current. After examining an auxiliary model of a particle in a rotating equatorial channel, it is shown that the zonal wavelength of the equatorial wave is linearly proportional to the equatorial length scale defined as , where is the equatorial value of the beta-parameter.

Flow of grounded abyssal ocean currents along zonally-varying topography on a rotating sphere

A steady nonlinear planetary–geostrophic model in spherical coordinates is presented describing the hemispheric-scale meridional flow of grounded abyssal currents on a zonally-sloping bottom. The model, which corresponds mathematically to a quasi-linear hyperbolic partial differential equation, can be solved explicitly for a cross-slope isopycnal field that is grounded (i.e. intersects the bottom on the up slope and down slope sides). As a consequence of the conservation of potential vorticity, the abyssal currents possess decreasing thickness in the equatorward direction while maintaining constant meridional volume transport. There is a small westward zonal transport in the interior of these currents that results in westward intensification as they flow toward the equator. Conditions for the possible formation of a shock to develop on the up slope flank of the current are derived.

Impact of parameterized lee wave drag on the energy budget of an eddying global ocean model

The impact of parameterized topographic internal lee wave drag on the input and output terms in the total mechanical energy budget of a hybrid coordinate high-resolution global ocean general circulation model forced by winds and air-sea buoyancy fluxes is examined here. Wave drag, which parameterizes the generation of internal lee waves arising from geostrophic flow impinging upon rough topography, is included in the prognostic model, ensuring that abyssal currents and stratification in the model are affected by the wave drag.An inline mechanical (kinetic plus gravitational potential) energy budget including four dissipative terms (parameterized topographic internal lee wave drag, quadratic bottom boundary layer drag, vertical eddy viscosity, and horizontal eddy viscosity) demonstrates that wave drag dissipates less energy in the model than a diagnostic (offline) estimate would suggest, due to reductions in both the abyssal currents and stratification. The equator experiences the largest reduction in energy dissipation associated with wave drag in inline versus offline estimates. Quadratic bottom drag is the energy sink most affected globally by the presence of wave drag in the model; other energy sinks are substantially affected locally, but not in their global integrals. It is suggested that wave drag cannot be mimicked by artificially increasing the quadratic bottom drag because the energy dissipation rates associated with bottom drag are not spatially correlated with those associated with wave drag where the latter are small. Additionally, in contrast to bottom drag, wave drag is a non-local energy sink.All four aforementioned dissipative terms contribute substantially to the total energy dissipation rate of about one terawatt. The partial time derivative of potential energy (non-zero since the isopycnal depths have a long adjustment time), the surface advective fluxes of potential energy, the rate of change of potential energy due to diffusive mass fluxes, and the conversion between internal energy and potential energy also play a non-negligible role in the total mechanical energy budget. Reasons for the <10% total mechanical energy budget imbalance are discussed.

Currents in the Drake Passage by the observations in October–November of 2011

The currents in the Drake Passage are studied from the ADCP and CTD data acquired in a section across the Drake Passage in October-November of 2011 and from the satellite altimeter data. A complicated pattern of currents including eight jets of the Antarctic Circumpolar Current (ACC) and a system of slope and abyssal currents was found. The most interesting result is the discovery of several cyclonic and anticyclonic mesoscale eddies confined to the abyss. Some reasons explaining the generation of such eddies by the meandering of the ACC jets in the upper ocean layer are presented.

Evidence of Bottom-Trapped Currents in the Kuroshio Extension Region

Abstract As part of the Kuroshio Extension System Study, observations from five current meter moorings reveal that the abyssal currents are weakly bottom intensified. In the framework of linear quasigeostrophic flow, the best fitted vertical trapping depths range from 8 to 15 km in the absence of steep topography, but one mooring near an isolated seamount exhibited vertical trapping that was more pronounced and energetic with a vertical trapping depth of 5 km. The ratios of current speeds and geostrophic pressure streamfunctions at the sea surface compared to the bottom are 88% in the absence of steep topography, 63% near an isolated seamount, and overall on average 83% of their value at a reference depth of 5300 m. It is hypothesized that weakly depth-dependent eddies impinging upon topographic features introduce to the flow the horizontal length scales of the topography, and these smaller lateral scales are subject to bottom intensification.

Currents in the Western Drake Passage according to the observations in January of 2010

The Western Drake Passage current system is investigated using the CTD, LADCP, and SADCP data of the cross Drake section carried out in January 2010. A complicated current structure consisting of the six Antarctic Circumpolar Current (ACC) jets as well as the system of slope and abyssal currents was revealed. The most interesting result is the identification of the abyssal quasi-geostrophic spurts in the northern part that probably are generated by abyssal eddy fragments, which are an imperative part of the meandering ACC.

First bipolar benthic brooder

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 401:15-20 (2010) - DOI: https://doi.org/10.3354/meps08446 First bipolar benthic brooder Piotr Kuklinski1,2,*, David K. A. Barnes3 1Department of Zoology, Natural History Museum, Cromwell Road, London SW7 5BD, UK 2Institute of Oceanology, Polish Academy of Sciences, ul. Powstanców Warszawy 55, Sopot 81-712, Poland 3British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK *Email: kuki@iopan.gda.pl ABSTRACT: A bipolar distribution is one in which a taxon occurs at high northern and southern latitudes but is absent in the latitudes between. In spite of the large distance between the Arctic and Antarctic, there are records of biota with bipolar distributions, both currently and in the geological past. To date, combined morphological and genetic studies of organisms such as bacteria and foraminifera have confirmed the occurrence of some species in both polar regions. Bipolar genera and families are also known in larger invertebrates, e.g. in crustaceans and molluscs, and a recent Census of Marine Life report suggested that more than 200 metazoan species may have bipolar distributions. Here we investigated specimens of the the cheilostome bryozoan Callopora weslawski from both Arctic and Antarctic localities. To our knowledge this is the first benthic brooder to be found in both polar regions and is the first record of a species of Callopora in Antarctic waters. We used scanning electron microscopy and statistical analyses to confirm the morphological identity of individuals. The encrusting nature of the species, its distribution in the deep Weddell Sea and its rarity mean that genetic confirmation of bipolarity may take years or decades. Possible paths of distribution are discussed, including the Pangea break-up, Plio-Pleistocene glaciations, isothermal submergence via off-shelf or abyssal currents and anthropogenic transport. KEY WORDS: Bipolar · Arctic · Antarctic · Bryozoa · Biodiversity Full text in pdf format PreviousNextCite this article as: Kuklinski P, Barnes DKA (2010) First bipolar benthic brooder. Mar Ecol Prog Ser 401:15-20. https://doi.org/10.3354/meps08446 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 401. Online publication date: February 22, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Ekman destabilization of inertially stable baroclinic abyssal flow on a sloping bottom

Baroclinic abyssal currents on a sloping bottom, which are nonlinearly stable in the sense of Liapunov in the absence of dissipation, are shown to be destabilized by the presence of a bottom Ekman boundary layer for any positive value of the Ekman number. When the abyssal flow is baroclinically unstable, the dissipation acts to reduce the inviscid growth rates except near the marginal stability boundary where it acts to increase the inviscid growth rates. It is shown that when the abyssal flow is baroclinically stable, the Ekman destabilization corresponds to the kinematic wave phase velocity lying outside the range of the inertial topographic Rossby phase velocities. The transition mechanism described here might provide a dynamical bridge between the nonrotational roll-wave instability that can occur in supercritical abyssal overflows and frictionally induced destabilization in subinertial geostrophically balanced baroclinic abyssal currents. In addition, the theory presented here suggests a dissipation-induced destabilization mechanism for coastal downwelling fronts whose cross-slope potential vorticity gradient does not satisfy the necessary condition for baroclinic instability.

Currents in the Drake Passage based on observations in 2007

Currents in the Drake Passage are studied using the data of a hydrographic section along the Shackleton Transverse Ridge observed in November 2007. The distribution of the velocity component normal to the section was computed by two methods: (a) directly on the basis of the lowered acoustic Doppler current profiler (LADCP) data; (b) by the calculation of geostrophic currents based on the CTD data with estimating the depth averaged velocity on the basis of the LADCP data. The main results of the research are the relatively low estimated value of the Antarctic Circumpolar Current (ACC) transport, which accounts for 65–70% of the ACC transports in December 2003 and November 2005, and the confirmation of the existence of several abyssal currents confined to the deep passages of the bottom topography.

Deep flow and transport through the Ulleung Interplain Gap in the Southwestern East/Japan Sea

Deep circulation in the southwestern East/Japan Sea through the Ulleung Interplain Gap (UIG), a possible pathway for deep-water exchange, was directly measured for the first time. Five concurrent current meter moorings were positioned to effectively span the UIG between the islands of Ulleungdo to the west and Dokdo to the east. They provided a 495-day time series of deep currents below 1800 m depth spanning the full breadth of the East Sea Deep and Bottom Water flowing from the Japan Basin into the Ulleung Basin. The UIG circulation is found to be mainly a two-way flow with relatively weak southward flows directed into the Ulleung Basin over about two-thirds of the western UIG. A strong, persistent, and narrow compensating northward outflow occurs in the eastern UIG near Dokdo and is first referred to here as the Dokdo Abyssal Current. The width of the abyssal current is about 20 km below 1800 m depth. The low-frequency variability of the transports is dominated by fluctuations with a period of about 40 days for inflow and outflow transports. The 40-day fluctuations of both transports are statistically coherent, and occur almost concurrently. The overall mean transport of the deep water below 1800 m into the Ulleung Basin over the 16.5 months is about 0.005 Sv (1 Sv=10 6 m 3 s −1), with an uncertainty of 0.025 Sv indicating net transport is negligible below 1800 m through the UIG.