scholarly journals Large Reemergence of Anthropogenic Carbon into the Ocean’s Surface Mixed Layer Sustained by the Ocean’s Overturning Circulation

2017 ◽  
Vol 30 (21) ◽  
pp. 8615-8631 ◽  
Author(s):  
Katsuya Toyama ◽  
Keith B. Rodgers ◽  
Bruno Blanke ◽  
Daniele Iudicone ◽  
Masao Ishii ◽  
...  
Keyword(s):  
Gas Exchange ◽  
Ocean Circulation ◽  
Mixed Layer ◽  
World Ocean ◽  
Diagnostic Tools ◽  
Water Volume ◽  
Surface Mixed Layer ◽  
Overturning Circulation ◽  
Carbon Cycle Model ◽  
Anthropogenic Carbon

We evaluate the output from a widely used ocean carbon cycle model to identify the subduction and obduction (reemergence) rates of anthropogenic carbon (Cant) for climatological conditions during the World Ocean Circulation Experiment (WOCE) era in 1995 using a new set of Lagrangian diagnostic tools. The principal scientific value of the Lagrangian diagnostics is in providing a new means to connect Cant reemergence pathways to the relatively rapid renewal time scales of mode waters through the overturning circulation. Our main finding is that for this model with 2.04 PgC yr−1 of uptake of Cant via gas exchange, the subduction and obduction rates across the base of the mixed layer (MLbase) are 4.96 and 4.50 PgC yr−1, respectively, which are twice as large as the gas exchange at the surface. Given that there is net accumulation of 0.17 PgC yr−1 in the mixed layer itself, this implies the residual downward Cant transport of 1.40 PgC yr−1 across the MLbase is associated with diffusion. Importantly, the net patterns for subduction and obduction transports of Cant mirror the large-scale patterns for transport of water volume, thereby illustrating the processes controlling Cant uptake. Although the net transfer across the MLbase by compensating subduction and obduction is relatively smaller than the diffusion, the localized pattern of Cant subduction and obduction implies significant regional impacts. The median time scale for reemergence of obducting particles is short (<10 yr), indicating that reemergence should contribute to limiting future carbon uptake through its contribution to perturbing the Revelle factor for surface waters.

Characteristics and variability of ocean ventilation in the high-latitude North Atlantic in an eddy-permitting ocean model

2021 ◽  
Author(s):  
Helen L. Johnson ◽  
Graeme MacGilchrist ◽  
David P. Marshall ◽  
Camille Lique ◽  
Matthew Thomas ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Mixed Layer ◽  
North Atlantic ◽  
High Latitude ◽  
Circulation Model ◽  
Open Ocean ◽  
Labrador Sea ◽  
Surface Mixed Layer ◽  
Atmospheric Forcing ◽  
Boundary Current

&lt;p&gt;A substantial fraction of the deep ocean is ventilated in the high latitude North Atlantic. As a result, the region plays a crucial role in transient climate change through the uptake of carbon dioxide and heat. We investigate the nature of ventilation in the high latitude North Atlantic in an eddy-permitting numerical ocean circulation model using a set of comprehensive Lagrangian trajectory experiments. Backwards-in-time trajectories from a model-defined &amp;#8216;North Atlantic Deep Water&amp;#8217; (NADW) reveal the times and locations of subduction from the surface mixed layer at high temporal and spatial resolution. The major fraction (&amp;#8764;60%) of NADW ventilation results from subduction directly into the Labrador Sea boundary current, with a smaller fraction (&amp;#8764;25%) arising from open ocean deep convection in the Labrador Sea. There is a notable absence of ventilation arising from subduction in the Greenland&amp;#8211;Iceland&amp;#8211;Norwegian Seas, due to the re-entrainment of those waters as they move southward. Temporal variability in ventilation arises both from changes in subduction &amp;#8212; driven by large-scale atmospheric forcing &amp;#8212; and from year-to-year changes in the subsurface retention of newly subducted water, the result of an inter-annual equivalent of Stommel&amp;#8217;s mixed layer demon. This interannual demon operates most effectively in the open ocean where newly subducted water is slow to escape its region of subduction. Thus, while subduction in the boundary current dominates NADW ventilation, processes in the open ocean set the variability, mediating the translation of inter-annual variations in atmospheric forcing to the ocean interior.&lt;/p&gt;

scholarly journals A Numerical Analysis on Coral Larval Networks across Reef Areas on the Northwest Coast of Okinawa Main Island, Japan

2021 ◽  
Vol 945 (1) ◽  
pp. 012030
Author(s):  
Kimika Takeyasu ◽  
Yusuke Uchiyama ◽  
Xu Zhang ◽  
Kosei Matsushita ◽  
Satoshi Mitarai
Keyword(s):  
High Resolution ◽  
Ocean Circulation ◽  
Mixed Layer ◽  
Short Distance ◽  
Northwest Coast ◽  
Surface Mixed Layer ◽  
Lagrangian Particle ◽  
Coral Larvae ◽  
Main Island ◽  
Tracking Model

Abstract Coral bleaching has recently occurred extensively over the world’s oceans, primarily due to high water temperatures. Mesophotic corals that inhabit at depths of approximately 30–150 m are expected to survive during bleaching events and to reseed shallow water corals afterward. In particular, in Okinawa, Japan, mesophotic coral ecosystems (MCEs) have been reported to serve as a refuge to preserve genotypic diversities of bleaching-sensitive corals. Connectivity of larval populations between different habitats is a key element that determines the area to be conserved for desirable coral ecosystems. Coral larvae generally behave passively to the surrounding currents and are transported by the advective and dispersive effects of ambient ocean currents. Thus, numerical ocean circulation models enable us to quantify connectivity with detailed spatiotemporal network structures. Our aim in this study is to quantify the short-distance and vertical connectivity of coral larvae in reef areas on the northwest coast of Okinawa Main Island. For the reason that both short-distance and vertical larval transport are influenced by complex nearshore topography, a very high-resolution 3-D circulation model is required. Therefore, we developed a quadruple nested high-resolution synoptic ocean model at a lateral spatial resolution of 50 m, coupled with an offline 3-D Lagrangian particle-tracking model. After validation of the developed model, short-distance horizontal coral connectivity across reef areas on the northwest coast was successfully evaluated. Furthermore, a series of Lagrangian particle release experiments were conducted to identify the vertical coral migration and 3-D connectivity required for the preservation of MCEs. The model revealed that coral larvae released from the semi-enclosed areas tended to remain near the source area, whereas they were diffused and dispersed gradually with time. The mesophotic corals were dispersed vertically to the deeper zone below the mixed layer, while upward transport occurred to induce the mesophotic corals to emerge near the surface, under the influence of the surface mixed layer. The model results solidly indicated significant connectivity between MCEs and shallow coral ecosystems.

scholarly journals Testing eddy compensation and eddy saturation in the Southern Ocean

2021 ◽  
Author(s):  
Dan Jones
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Ocean Circulation ◽  
World Ocean ◽  
Global Ocean ◽  
Future Climate Change ◽  
Overturning Circulation ◽  
Dynamic Component ◽  
Cold Temperatures ◽  
Decadal Scale

The Southern Ocean (SO) is a unique and dynamic component of the climate system. Due in part to its cold temperatures and large surface area, the SO is an important region for the transfer of heat, momentum, and climatically relevant gases between the atmosphere and the interior ocean. The strong westerly winds above the SO help drive a powerful current (i.e. the Antarctic Circumpolar Current or ACC) that connects Earth's ocean basins in a global overturning circulation. In recent decades, these winds have strengthened and shifted poleward. Despite this change in surface forcing, no clear observational signal of the oceanic density structure's response has yet been detected. The eddy compensation hypothesis posits that changes in the direct wind-driven overturning circulation are balanced by changes in the eddy-induced meridional circulation, effectively rendering SO stratification insensitive to wind stress. The closely related (but not identical) eddy saturation hypothesis suggests that the ACC is also insensitive to increased wind stress, since additional energy ends up in the mesoscale eddy field instead of in the zonal mean circulation. In this work, we examine the viability of the eddy compensation and saturation hypotheses on interannual, decadal, and centennial timescales. Using a combination of theory and idealized numerical simulations, we show that it may take the Southern Ocean many decades to centuries to fully equilibrate with the world ocean following a change in wind stress. As such, it may be difficult to detect changes in isopycnal slope using the few decades of available observational data. We also explore the characteristics of eddy-driven interannual variability and examine how this variability may affect the decadal-scale adjustment of the global ocean. Our results suggest that departures from the eddy compensation regime may be important on decadal and centennial timescales, on which the interaction between regional Southern Ocean circulation and global ocean circulation is significant. As such, we suggest that Southern Ocean overturning circulation is likely to strengthen in response to recent and future climate change, with implications for the global carbon cycle and climate.

scholarly journals An Objective Method for Determining Ocean Mixed Layer Depth with Applications to WOCE Data

2018 ◽  
Vol 35 (3) ◽  
pp. 441-458 ◽  
Author(s):  
Peng-Qi Huang ◽  
Yuan-Zheng Lu ◽  
Sheng-Qi Zhou
Keyword(s):  
Ocean Circulation ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Random Noise ◽  
World Ocean ◽  
New Method ◽  
Layer Depth ◽  
Density Profiles ◽  
Relative Variance ◽  
Maximum Angle

AbstractA new method is developed to identify the mixed layer depth (MLD) from individual temperature or density profiles. A relative variance profile is obtained that is the ratio between the standard deviation and the maximum variation of the temperature (density) from the sea surface, and the depth of the minimum relative variance is defined as the MLD. The new method is robust in finding the MLD under the influence of random noise (noise level ≤ 5%). A comparison with other available methods, which include the threshold (difference, difference interpolation, gradient, and hybrid methods) and objective (curvature and maximum angle methods) methods, is carried out using the World Ocean Circulation Experiment (WOCE) data. It is found that for a variety of depth sampling resolutions ranging from 0.04 to 25 dbar, the new method and the difference-interpolation method predict MLD values that are closer to the visually inspected ones than those by other methods. Moreover, the quality index (QI) of the MLD that is determined by the new method is the highest when compared with those of the available methods. Also, the application of the new method on the WOCE global dataset yields 94% of MLD values with , substantially higher than those (≤86%) of other methods. Ultimately, it is found that the new method determines very similar MLD values when applied to temperature or density profiles globally because it identifies the base of the mixed layer rather than the uppermost depth of the thermocline. This unique advantage makes the new method applicable in many cases, especially when the density profile is unavailable.

ON EVALUATION OF THE ROLE OF THERMAL AND WIND FACTORS FOR A PHYSICAL MODEL OF THE WORLD OCEAN GENERAL CIRCULATION SYSTEM

2019 ◽  
Vol 47 (3) ◽  
pp. 80-91
Author(s):  
V. G. Neiman
Keyword(s):  
Physical Model ◽  
Ocean Circulation ◽  
General Circulation ◽  
World Ocean ◽  
Circulation System ◽  
The Public ◽  
The World ◽  
Almost All ◽  
Conceptual Foundations

The main content of the work consists of certain systematization and addition of longexisting, but eventually deformed and partly lost qualitative ideas about the role of thermal and wind factors that determine the physical mechanism of the World Ocean’s General Circulation System (OGCS). It is noted that the conceptual foundations of the theory of the OGCS in one form or another are contained in the works of many well-known hydrophysicists of the last century, but the aggregate, logically coherent description of the key factors determining the physical model of the OGCS in the public literature is not so easy to find. An attempt is made to clarify and concretize some general ideas about the two key blocks that form the basis of an adequate physical model of the system of oceanic water masses motion in a climatic scale. Attention is drawn to the fact that when analyzing the OGCS it is necessary to take into account not only immediate but also indirect effects of thermal and wind factors on the ocean surface. In conclusion, it is noted that, in the end, by the uneven flow of heat to the surface of the ocean can be explained the nature of both external and almost all internal factors, in one way or another contributing to the excitation of the general, or climatic, ocean circulation.

Mixed Layer Models and Their Application to Water Quality Problems

1994 ◽  
Vol 29 (2-3) ◽  
pp. 221-232
Author(s):  
M.J. McCormick
Keyword(s):  
Water Quality ◽  
Mixed Layer ◽  
Thermal Structure ◽  
Mass Conservation ◽  
Eddy Diffusion ◽  
Rate Of Change ◽  
Surface Mixed Layer ◽  
Storm Events ◽  
Quality Model ◽  
Mixing Processes

Abstract Four one-dimensional models which have been used to characterize surface mixed layer (ML) processes and the thermal structure are described. Although most any model can be calibrated to mimic surface water temperatures, it does not imply that the corresponding mixing processes are well described. Eddy diffusion or "K" models can exhibit this problem. If a ML model is to be useful for water quality applications, then it must be able to resolve storm events and, therefore, be able to simulate the ML depth, h, and its time rate of change, dh/dt. A general water quality model is derived from mass conservation principles to demonstrate how ML models can be used in a physically meaningful way to address water quality issues.

scholarly journals Simulation of diurnal variability in vertical density structure using a coupled model

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
B. Yadidya ◽  
A. D. Rao ◽  
Sachiko Mohanty
Keyword(s):  
Mixed Layer ◽  
3D Model ◽  
Coupled Model ◽  
Wave Model ◽  
Andaman Sea ◽  
Surface Mixed Layer ◽  
Diurnal Variability ◽  
Rama Buoy ◽  
Vertical Displacements ◽  
Primary Advantage

AbstractThe changes in the physical properties of the ocean on a diurnal scale primarily occur in the surface mixed layer and the pycnocline. Price–Weller–Pinkel model, which modifies the surface mixed layer, and the internal wave model based on Garrett–Munk spectra that calculates the vertical displacements due to internal waves are coupled to simulate the diurnal variability in temperature and salinity, and thereby density profiles. The coupled model is used to simulate the hourly variations in density at RAMA buoy (15° N, 90° E), in the central Bay of Bengal, and at BD12 (10.5° N, 94° E), in the Andaman Sea. The simulations are validated with the in-situ observations from December 2013 to November 2014. The primary advantage of this model is that it could simulate spatial variability as well. An integrated model is also tested and validated by using the output of the 3D model to initialize the coupled model during January, April, July, and October. The 3D model can be used to initialize the coupled model at any given location within the model domain to simulate the diurnal variability of density. The simulations showed promising results which could be further used in simulating the acoustic fields and propagation losses which are crucial for Navy operations.

scholarly journals Galápagos upwelling driven by localized wind–front interactions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alexander Forryan ◽  
Alberto C. Naveira Garabato ◽  
Clément Vic ◽  
A. J. George Nurser ◽  
Alexander R. Hearn
Keyword(s):  
Ocean Circulation ◽  
Realistic Model ◽  
Surface Mixed Layer ◽  
Equatorial Pacific Ocean ◽  
World Heritage Sites ◽  
Theory Of Evolution ◽  
Heritage Sites ◽  
Galapagos Archipelago ◽  
Eastern Equatorial Pacific ◽  
Eastern Equatorial Pacific Ocean

AbstractThe Galápagos archipelago, rising from the eastern equatorial Pacific Ocean some 900 km off the South American mainland, hosts an iconic and globally significant biological hotspot. The islands are renowned for their unique wealth of endemic species, which inspired Charles Darwin’s theory of evolution and today underpins one of the largest UNESCO World Heritage Sites and Marine Reserves on Earth. The regional ecosystem is sustained by strongly seasonal oceanic upwelling events—upward surges of cool, nutrient-rich deep waters that fuel the growth of the phytoplankton upon which the entire ecosystem thrives. Yet despite its critical life-supporting role, the upwelling’s controlling factors remain undetermined. Here, we use a realistic model of the regional ocean circulation to show that the intensity of upwelling is governed by local northward winds, which generate vigorous submesoscale circulations at upper-ocean fronts to the west of the islands. These submesoscale flows drive upwelling of interior waters into the surface mixed layer. Our findings thus demonstrate that Galápagos upwelling is controlled by highly localized atmosphere–ocean interactions, and call for a focus on these processes in assessing and mitigating the regional ecosystem’s vulnerability to 21st-century climate change.

Sign in / Sign up

Export Citation Format

Share Document