Net Heat Transport Research Articles

The Bering Strait Throughflow Component of the Global Mass, Heat and Freshwater Transport

AbstractAs the only oceanic connection between the Pacific and Arctic‐Atlantic Oceans, Bering Strait throughflow carries a climatological northward transport of about 1 Sv, contributing to the Atlantic Meridional Overturning Circulation (AMOC). Here, Lagrangian analysis quantifies the global distributions of volume transport, transit‐times, thermohaline properties, diapycnal transformation, heat and freshwater transports associated with Bering Strait throughflow. Virtual Lagrangian parcels, released at Bering Strait, are advected by the velocity of Estimating the Circulation and Climate of the Ocean, backward and forward in time. Backward trajectories reveal that Bering Strait throughflow enters the Pacific basin on the southeast side, as part of fresh Antarctic Intermediate Water, then follows the wind‐driven circulation to Bering Strait. Median transit time from S in Indo‐Pacific to Bering Strait is 175 years. Sixty‐four percent of Bering Strait throughflow enters the North Atlantic through the Labrador Sea. The remaining 36% flows through the Greenland Sea, warmed and salinified by the northward flowing Atlantic waters. Deep water formation of water flowing through Bering Strait occurs predominantly in the Labrador Sea. Subsequently, this water joins the lower branch of AMOC, flowing southward in the deep western boundary current as North Atlantic Deep Water. Median transit time from Bering Strait to S in South Atlantic is 160 years. The net heat transport of Bering Strait throughflow is northward everywhere, and net freshwater transport by Bering Strait throughflow is mostly northward. The freshwater transport is largest in the subpolar region of basin sectors: northward in the Pacific and Arctic and southward in the Atlantic.

High-resolution numerical modelling of seasonal volume, freshwater, and heat transport along the Indian coast

Abstract. Seasonal reversal of winds and equatorial remote forcing influences the circulation of the Arabian Sea (AS) and Bay of Bengal (BoB) basins in the northern Indian Ocean. In this study, we numerically modelled the physical characteristics of the AS and BoB, using the Massachusetts Institute of Technology general circulation model (MITgcm) at a high spatial resolution of 1/20° forced with climatological initial and boundary conditions. The simulated temperature, salinity, and flow fields were validated with satellite and in situ datasets. We then studied the exchange of coastal waters by evaluating transports computed from the model simulations. The alongshore volume transport on the eastern coast is stronger with high seasonal variability due to the poleward-flowing western boundary current and equatorward-flowing East Indian Coastal Current. West coast transport is influenced by large intraseasonal oscillations. The alongshore freshwater transport is an order less than the alongshore volume transport. Out of the net volume transport, freshwater accounts for a maximum of 6.03 % during the southwestern monsoon season, followed by 4.85 % in the post-monsoon season. We observe an inverse relationship between alongshore freshwater and volume transport on the western coast and a direct relationship on the eastern coast. The contribution of eddy-induced heat and freshwater transport was also examined. The relation between net heat transport and net heat flux illustrates the role of coastal currents and equatorial forcing in dissipating heat within the coastal waters. We observed that meridional heat transport over the AS is stronger than over the BoB. Both basins act as a heat source during the summer monsoon and heat sink during the winter. This high-resolution model setup simulates all the important physical climatological patterns, leading to a better understanding of the state of the northern Indian Ocean.

Mean‐State and Seasonal Variability in Temperature Structure and Heat Transport in the East Australian Current System From a Multi‐Decadal Regional Ocean Model

AbstractWestern Boundary Currents (WBCs) such as the East Australian Current (EAC) are vital for moving heat from low to high latitudes, controlling regional weather and global climate. Previous EAC System studies have provided a general overview of temperature variability and heat transport, but they lacked spatial and seasonal detail. Using a high‐resolution, 26‐year‐long ocean model simulation, we systematically characterize the seasonal variability and structure in key temperature metrics and heat transport in the EAC System. Our findings reveal a clear seasonal cycle with a poleward expansion of key variables in summer (mean and eddy kinetic energy, upper ocean heat content, heat transport) and contraction equatorward with reductions in winter. We show that the dynamical regime transition, from jet to eddy‐dominated at the EAC separation zone (S), modifies the net meridional heat transport. Upstream of separation, transport is poleward, with some zonal input of heat. Downstream of EAC separation, there is an increase in heat recirculation by mesoscale eddies combined with a smaller zonal export of heat. This study highlights the significance of resolving spatio‐temporal variability in WBC systems driven by mesoscale dynamics, which will have implications for the representation of critical dynamics in future climate models.

Hydrodynamic and atmospheric drivers create distinct thermal environments within a coral reef atoll

Within coral reefs, different thermal environments can be found at locations separated by less than 100 s of meters and can generate fine-scale patterns of thermal stress and subsequent bleaching. In this study, we use an 11-month record of in situ temperature measurements, coupled with oceanographic and atmospheric data to examine the role of surface and advective heat fluxes in driving spatial patterns of temperature variability across several reef zones (i.e., fore-reef, reef flat, channel and lagoon) within an individual coral reef atoll. We show that advection of heat (driven by a combination of wave and tidal flows) was dominant across all sites and surface heating was more important across shallow areas or areas of low net exchange (i.e., reef flat and lagoon zones). Tidal flows were important in driving short term variability in the transport of heat across the atoll, but their contribution to the net transport of heat (cooling vs heating) was less significant over the longer timescales (days to weeks) that are typically used to assess thermal stress experienced by coral reef communities (e.g., Degree Heating Weeks). Conversely, although the wave-driven advection of heat contributed minimally to reef temperature changes over short timescales, the net transport of heat over daily to weekly timescales had a significant influence on persistent temperature anomalies. By parameterising the mechanisms driving temperature variability across the reef flat and lagoon zones, we demonstrate how satellite measurements of sea surface temperatures can be corrected to provide robust temperature estimates at the reef scale.

Cross-shelf exchange associated with a shelf-water streamer at the Mid-Atlantic Bight shelf edge

Significant exchanges between the Mid-Atlantic Bight (MAB) continental shelf and the neighboring open ocean can be induced by shelf water streamers, submesoscale filaments of shelf water entrained into the open ocean by Gulf Stream warm-core rings (WCRs) impinging onto the MAB continental shelf. Shelf water streamers have distinctive surface temperature and chlorophyll signals, and are thus visible from space. Satellite-measured sea surface height, temperature and chlorophyll show the evolution of a WCR over its 6-month lifespan in February-August 2019 and the persistent shelf water streamer it generated on its outskirt. In situ measurements from a two-week cruise in July 2019 were analyzed to investigate the physical, biological and biogeochemical characteristics of the shelf water streamer below the surface, and to quantify the associated cross-shelf transport of volume, heat, salt, carbon and oxygen. The analyses demonstrated that offshore transport of shelf water by the streamer, which was presumably balanced by either onshore intrusion of ring water or enhanced transport of shelf water from upstream, represented a major form of exchange between the MAB continental shelf and the open ocean. The streamer caused significant net onshore transport of heat and salt, and a significant net offshore transport of organic carbon and oxygen. Primary productivity in the streamer was higher than the surrounding slope and ring waters on the surface, which likely resulted from subsurface nutrients in the offshore-flowing shelf water being gradually consumed as the overlying water became clearer. WCR-induced shelf water streamers thus enhanced surface biological productivity in the slope sea.Plain Language Summary: Waters of the shallow Mid-Atlantic Bight continental shelf and the neighboring deep slope sea have distinctly different physical, biological and chemical properties. Mixing between them can affect the shelf ecosystem and the dispersal of coastal materials into the deep ocean. One type of cross-shelf-edge mixing process results from strong clockwise-rotating vortices – so-called warm-core rings – formed from meanders of the Gulf Stream. As a warm-core ring intrudes onto the shelf edge, it often draws shelf water offshore, forming a thin filament in the slope sea. This filament is called a shelf-water streamer and has distinctive surface temperature and chlorophyll signals that are visible from space. Warm-core rings can also push offshore water onto the shallow shelf. This study examines the evolution of a warm-core ring over its 6-month lifespan in 2019 and the shelf-water streamer the ring induced in 5 of the 6 months. Interdisciplinary measurements from a field expedition in July 2019 were examined to assess the subsurface patterns of the streamer and to quantify the induced cross-shelf fluxes of heat, salt, organic carbon and oxygen. The analysis showed that the streamer represented a major form of cross-shelf mixing and caused a substantial onshore transport of heat and salt, as well as a substantial offshore transport of organic carbon and oxygen.

Wind-Induced Variability of Warm Water on the Southern Bellingshausen Sea Continental Shelf.

The Bellingshausen Sea hosts heat transport onto the continental shelf, potentially enhancing ice shelf basal melt. Here, we use the GLORYS12V1 1993-2018 reanalysis to identify physical processes that set seasonal and interannual variability of water mass properties in the Eltanin and Latady Bays on the southern Bellingshausen Sea continental shelf. Annual means of potential temperature from 300m to the seabed reveal interannual variability and allow separation into warm and cold regimes. The Amundsen Sea Low (ASL) is more intense and extends further east during the warm regime than the cold regime. In the warm regime, a wind-induced reduction of sea ice concentration near the coast increases surface heat loss, convection, and formation of cold dense water in winter, associated with a decrease in heat content of the southern Bellingshausen Sea over time and a net northward heat transport. In contrast, in the cold regime, increased sea ice concentration reduces surface heat loss and thus formation of cold, dense water. Combined with an increase in heat content over time and a net southward heat transport, this results in a warming of the southern Bellingshausen Sea. This suggests that variability in the deep water temperature in the southern Bellingshausen Sea is primarily due to local surface heat fluxes above the shelf. The variability of surface heat fluxes is related to the variability of the ASL and its influence on sea ice extent and local formation of cold, dense water in winter.

Coupled modeling of peatlands carbon cycle and carbon dioxide emission from their peat deposits

COmplex Model of BOg LAndscapes (COMBOLA) is a set of dynamic models of carbon and nitrogen turnover, net ecosystem exchange, water balance, heat and water transport, generation and transfer of CO2 and CH4 in a peat deposit on a number of time scales. Combined modeling of carbon turnover and carbon dioxide emission from peat deposits on an annual time scale is carried out as part of COMBOLA for several bog landscapes in Western-Siberian south taiga. One-dimensional vertical reaction-diffusion model for carbon dioxide emission from peat deposit is combined with compartment carbon cycle model allowing estimate both bog type vegetation changes and greenhouse gases balance under probable climate change or perturbations initiated by human activities. Water table level (WTL) separating aerobic peat layer from the anaerobic one is calculated by means of the whole peat layer depth and its water balance relations. Minimal statistical information is used for calibrating temperature dependencies together with coefficients of heat and water transfer equations. The stationary states of carbon cycle are accompanied by steady average profiles of carbon dioxide concentration and can loose stability under human or climatic perturbations. The model dynamics is simulated with several climatic projections of the IPSL atmospheric circulation model for 21st century with anthropogenic scenarios RCP-2.6 and RCP-8.5.

The redistribution of anthropogenic excess heat is a key driver of warming in the North Atlantic

Understanding ocean excess heat uptake is crucial for assessing climate warming, yet uncertainties remain about its history and redistribution. Here, we reconstruct ocean heat content change along the 25°N Atlantic hydrographic section and assess its spatiotemporal origin and fate. We show that the delayed response of the ocean below 700 m to sea surface temperature change contribute to 62% of full depth warming at this latitude for 1850–2018, falling to 35% for 1975–2018 when anthropogenic warming in the upper ocean accelerated. The regional climate fluctuations shape ocean heat content variability at 25°N with contributions from the Labrador Sea producing most of the decadal variability and the Nordic Seas bound to become the main contributor to deep ocean warming in the coming decades. Chiefly, the net excess heat transport across 25°N has increased recently, warming the domain north of 25°N at a rate of 0.89 ± 0.19 W m−2 during 2012–2018, revealing that excess heat redistribution is a key driver of North Atlantic heat gain.

Submesoscale Ageostrophic Motions Within and Below the Mixed Layer of the Northwestern Pacific Ocean

AbstractSubmesoscale dynamics below the mixed layer (ML) and their mechanisms are still unclear. By a series of nested simulations in the Pacific Northwest with high horizontal resolution of ∼500 m, this study reveals that there exist strong submesoscale ageostrophic motions in the upper pycnocline of the Kuroshio Extension region. These motions exhibit enhanced lateral buoyancy gradient and vigorous vertical velocity but with weak vertical vorticity distinct from the ML submesoscale activities. The vertical velocity in the high‐resolution simulation reaches tens of meters per day, consistent with recent observations (e.g., SubMESI and OSMOSIS). Our analysis shows that the enhanced vertical velocity is mostly attributed to the along‐isopycnal motions at the Kuroshio front, but in the region nearby the large vertical velocity mostly arises from the wave‐like vertical movement of isopycnals. To understand the mechanisms for the large vertical velocity, this paper further examined the instability of the flow and the frequency‐wavenumber spectra of vertical vorticity, lateral divergence, lateral buoyancy gradient, and vertical velocity. A criterion based on the ratio between divergence and vorticity variance in spectral space is used to roughly identify the upper bound of unbalanced submesoscales. The results suggest that the high‐frequency, high‐wavenumber processes dominate the vertical motions within and below the ML and significantly enhance the net vertical heat transport between the ML and the ocean interior. This study seeks to provide comprehension of the submesoscale ageostrophic motions below the ML and their impacts on the upper ocean.

The thermodynamic and dynamic control of the sensible heat polynya in the western Cosmonaut Sea

A prominent feature in the west Cosmonaut Sea is the reoccurrence of a sensible heat polynya — the western Cosmonaut Sea Polynya (wCSP), which normally exists in late austral autumn and early winter. The Southern Ocean Sate Estimate (SOSE) reanalysis product is employed to investigate the thermodynamic and dynamic processes controlling the formation and evolution of a real wCSP event in 2009, when the polynya properties revealed from satellite observations are reasonably simulated by SOSE. An oceanic heat budget analysis was conducted for the surface layer above the thermocline, and the results reveal that heat advection is the major term contributing to the surface heat content variation in this area. The precursor of wCSP — an embayment — was formed during cyclonic atmospheric circulations. The negative wind stress curl from a cyclone induced upwelling that brought the warm circumpolar deep water to the surface and presumably melted ice. Meanwhile, the location of the cyclone relative to the wCSP created weaker easterlies over the northern boundary of polynya and stronger easterlies over the southern boundary of polynya. This leads to difference in the meridional oceanic heat transports across the northern and southern boundaries, resulting in net positive meridional oceanic heat transport into the polynya. Both the vertical heat advection and the meridional heat advection contribute significantly to increased heat content in the surface layer of wCSP, causing sea-ice melt and formation of the embayment. The cyclonic wind field promotes convergence of sea ice over the northern area of the embayment and results in the polynya. The formation of wCSP is likely related to the strength and position of Southern Annular Mode on interannual scale, and may potentially affect the biological productivity by controlling the availability of light in the mixed layer.

Sustained Decadal Warming Phase in the Southwestern Indian Ocean since the Mid-1990s

Regardless of the slowdown in global warming during the hiatus period, sea surface temperatures (SSTs) in the southwestern Indian Ocean (SWIO) have experienced sustained decadal warming for more than two decades since the mid-1990s. The SWIO SSTs warmed steadily during 1996–2016, causing a warming hot spot of 0.4 K decade−1 in a large region east of Madagascar. An upper-layer heat budget analysis indicated that heat advection by ocean currents was the greatest contributor to the warming of the SWIO SSTs. The existence of an anticyclonic geostrophic current along the western boundary of the SWIO tended to maintain such warming by transporting warmer water from the west into the SWIO region. In addition, net positive heat transport by ocean currents also occurred at the southern boundary of the SWIO as the climatological northward transport of cold water from the Southern Ocean weakened. This reduction in northward ocean currents at the surface was caused by local wind stress changes, leading to a southward Ekman current. Below the surface, an anticyclonic geostrophic current pattern existed around the warming center near the southeastern SWIO, which reduced the transport of cold waters from the Southern Ocean and warmed the SWIO. These processes near the two boundaries formed a self-sustaining positive feedback mechanism and favored the maintenance of sustained warming in the SWIO. More attention is needed to analyze the sustained long-lasting warming in the SWIO, as it is a unique phenomenon occurring under the background of the ongoing global warming.

Heat budget responses of the eastern China seas to global warming in a coupled atmosphere-ocean model

Impacts of climate change on heat budget in the Eastern China Seas (ECSs) are estimated under the historical, RCP4.5 and RCP8.5 scenarios using an atmosphere-ocean coupled regional climate model system (REMO/MPIOM). The results suggest that the recent and future ocean warming over the ECSs is linked overall to an increased oceanic heat transport by currents, which is partly compensated by the air-sea heat exchange. The Taiwan Strait is the major source of oceanic heat into the ECSs, whereas the shelf break section (SBS) acts as a heat sink. An increased net oceanic heat transport into the ECSs is projected under both considered RCP scenarios, mainly resulting from a reduction of the outward heat transport through the SBS. The mean relative contribution of SBS to the oceanic heat transport thus decreases by 4%–5% under both RCP scenarios, relative to historical run. Regarding the surface air-sea exchange, the heat loss caused by thermal radiation, latent and sensible heat in the ECSs exceeds the heat gain achieved by solar radiation. Under the RCP scenarios, warmer SST and stronger surface wind will enhance the upward latent heat flux, eventually leading to a more pronounced heat loss from the ECSs. The mean relative contributions of the latent heat flux to the air-sea heat exchange notably increases by 2%–3% under both projection scenarios, relative to historical run. Taking into account all components of the ECSs heat balance, we deduce that the increased horizontal heat transport will enhance the surface evaporation over the ECSs under future warming.

A new formulation of heat dissipation in a rocking Büttiker-Landauer ratchet model

Thermal ratchets achieve net particle transport through recti cation of thermal uctuations, which arise from one or more heat baths in the system. We propose a new formulation of heat dissipation from the ratchet to the thermal baths, using a rocking Büttiker-Landauer ratchet model. We found that heat transport between the ratchet and the heat baths is related to the effective temperature through the generalization of the uctuation-dissipation theorem for systems far from equilibrium. We showed that the net heat transport between the ratchet and the heat baths is different from Fourier’s law and is the sum of two terms which are proportional to the nth power of the difference between the effective temperature of ratchet and the temperature of the baths. The power n depends only on the temperature of the bath, while the thermal conductivity also depends on the ratchet potential. These ndings suggest that anomalous heat dissipation can be a non-equilibrium measure for systems far from equilibrium.

Heat, salt, and volume transports in the eastern Eurasian Basin of the Arctic Ocean from 2 years of mooring observations

Abstract. This study discusses along-slope volume, heat, and salt transports derived from observations collected in 2013–2015 using a cross-slope array of six moorings ranging from 250 to 3900 m in the eastern Eurasian Basin (EB) of the Arctic Ocean. These observations demonstrate that in the upper 780 m layer, the along-slope boundary current advected, on average, 5.1±0.1 Sv of water, predominantly in the eastward (shallow-to-right) direction. Monthly net volume transports across the Laptev Sea slope vary widely, from ∼0.3±0.8 in April 2014 to ∼9.9±0.8 Sv in June 2014; 3.1±0.1 Sv (or 60 %) of the net transport was associated with warm and salty intermediate-depth Atlantic Water (AW). Calculated heat transport for 2013–2015 (relative to −1.8 ∘C) was 46.0±1.7 TW, and net salt transport (relative to zero salinity) was 172±6 Mkg s−1. Estimates for AW heat and salt transports were 32.7±1.3 TW (71 % of net heat transport) and 112±4 Mkg s−1 (65 % of net salt transport). The variability of currents explains ∼90 % of the variability in the heat and salt transports. The remaining ∼10 % is controlled by temperature and salinity anomalies together with the temporal variability of the AW layer thickness. The annual mean volume transports decreased by 25 % from 5.8±0.2 Sv in 2013–2014 to 4.4±0.2 Sv in 2014–2015, suggesting that changes in the transports at interannual and longer timescales in the eastern EB may be significant.

Complex bog landscape model (COMBOLA) as an integrated tool for modeling of biotic turnover and peat deposit processes

Biotic cycling in ecosystems consists of live organic matter production and dead organic matter destruction. The latter is accompanied by the emission of greenhouse gases into the atmosphere. In peatland landscapes, additional conditions are imposed due to the presence of a water table depth (WTD), under which the destruction is anaerobic with methane generation, while above the WTD it is aerobic, and part of the diffusing methane is consumed by the methanotrophic bacteria. Hence, due to the complexity of heat and water transfer processes in the peat deposit and the nonlinearity of biological turnover, it is necessary to make a combination of their models. The COmplex Model of BOg LAndscapes (COMBOLA) is a set of dynamic models of carbon and nitrogen turnover, net ecosystem exchange, water balance, heat and water transport, generation and transfer of CO2 and CH4 in a peat deposit on annual, seasonal, and daily time scales. The main component includes a series of biotic turnover models – from a mass-balance equation on an annual time scale to a NEE dynamics model on a daily one. Biotic turnover can be represented by a single carbon cycle, a single nitrogen cycle or both. Another important component of the COMBOLA system is a one-dimensional vertical model of heat-water-gas exchange in a peat deposit. Thus, a number of interconnected modules constitute an integrated mathematical model of peatland landscapes adapted to any given initial information.

Microstructure Observations of Turbulent Heat Fluxes in a Warm-Core Canada Basin Eddy

AbstractAn intrahalocline eddy was observed on the Chukchi slope in September of 2015 using both towed CTD and microstructure temperature and shear sections. The core of the eddy was 6°C, significantly warmer than the surrounding −1°C water and far exceeding typical temperatures of warm-core Arctic eddies. Microstructure sections indicated that outside of the eddy the rate of dissipation of turbulent kinetic energy ε was quite low . However, at the edges of the eddy core, ε was elevated to . Three different processes were associated with elevated ε. Double-diffusive steps were found at the eddy’s top edge and were associated with an upward heat flux of 5 W m−2. At the bottom edge of the eddy, shear-driven mixing played a modest role, generating a heat flux of approximately 0.5 W m−2 downward. Along the sides of the eddy, density-compensated thermohaline intrusions transported heat laterally out of the eddy, with a horizontal heat flux of 2000 W m−2. Integrating these fluxes over an idealized approximation of the eddy’s shape, we estimate that the net heat transport due to thermohaline intrusions along the eddy flanks was 2 GW, while the double-diffusive flux above the eddy was 0.4 GW. Shear-driven mixing at the bottom of the eddy accounted for only 0.04 GW. If these processes continued indefinitely at the same rate, the estimated life-span would be 1–2 years. Such eddies may be an important mechanism for the transport of Pacific-origin heat, freshwater, and nutrients into the Canada Basin.

Circum‐Antarctic Shoreward Heat Transport Derived From an Eddy‐ and Tide‐Resolving Simulation

AbstractAlmost all heat reaching the bases of Antarctica's ice shelves originates from warm Circumpolar Deep Water in the open Southern Ocean. This study quantifies the roles of mean and transient flows in transporting heat across almost the entire Antarctic continental slope and shelf using an ocean/sea ice model run at eddy‐ and tide‐resolving (1/48°) horizontal resolution. Heat transfer by transient flows is approximately attributed to eddies and tides via a decomposition into time scales shorter than and longer than 1 day, respectively. It is shown that eddies transfer heat across the continental slope (ocean depths greater than 1,500 m), but tides produce a stronger shoreward heat flux across the shelf break (ocean depths between 500 m and 1,000 m). However, the tidal heat fluxes are approximately compensated by mean flows, leaving the eddy heat flux to balance the net shoreward heat transport. The eddy‐driven cross‐slope overturning circulation is too weak to account for the eddy heat flux. This suggests that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around Antarctica, though likely modulated by tides and surface forcing.

Impact of thermally dead volume on phonon conduction along silicon nanoladders.

Thermal conduction in complex periodic nanostructures remains a key area of open questions and research, and a particularly provocative and challenging detail is the impact of nanoscale material volumes that do not lie along the optimal line of sight for conduction. Here, we experimentally study thermal transport in silicon nanoladders, which feature two orthogonal heat conduction paths: unobstructed line-of-sight channels in the axial direction and interconnecting bridges between them. The nanoladders feature an array of rectangular holes in a 10 μm long straight beam with a 970 nm wide and 75 nm thick cross-section. We vary the pitch of these holes from 200 nm to 1100 nm to modulate the contribution of bridges to the net transport of heat in the axial direction. The effective thermal conductivity, corresponding to reduced heat flux, decreases from ∼45 W m-1 K-1 to ∼31 W m-1 K-1 with decreasing pitch. By solving the Boltzmann transport equation using phonon mean free paths taken from ab initio calculations, we model thermal transport in the nanoladders, and experimental results show excellent agreement with the predictions to within ∼11%. A combination of experiments and calculations shows that with decreasing pitch, thermal transport in nanoladders approaches the counterpart in a straight beam equivalent to the line-of-sight channels, indicating that the bridges constitute a thermally dead volume. This study suggests that ballistic effects are dictated by the line-of-sight channels, providing key insights into thermal conduction in nanostructured metamaterials.

Heat transport variation due to change of North Pacific subtropical gyre interior flow during 1993–2012

Applying segment-wise altimetry-based gravest empirical mode method to expendable bathythermograph temperature, Argo salinity, and altimetric sea surface height data in March, June, and November from San Francisco to near Japan (30∘ N, 145∘ E) via Honolulu, we estimated the component of the heat transport variation caused by change in the southward interior geostrophic flow of the North Pacific subtropical gyre in the top 700 m layer during 1993–2012. The volume transport-weighted temperature (T I) is strongly dependent on the season. The anomaly of T I from the mean seasonal variation, whose standard deviation is 0.14∘C, was revealed to be caused mainly by change in the volume transport in a potential density layer of 25.0−25.5σ 𝜃 . The anomaly of T I was observed to vary on a decadal or shorter, i.e., quasi-decadal (QD), timescale. The QD-scale variation of T I had peaks in 1998 and 2007, equivalent to the reduction in the net heat transport by 6 and 10 TW, respectively, approximately 1 year before those of sea surface temperature (SST) in the warm pool region, east of the Philippines. This suggests that variation in T I affects the warm pool SST through modification of the heat balance owing to the entrainment of southward transported water into the mixed layer.

Thermodynamics and hydrodynamics in an atoll reef system and their influence on coral cover

We present results of the thermodynamics and hydrodynamics of an atoll system and their effect on coral cover based on field measurements from 2012 to 2014 on Palmyra Atoll in the central Pacific. We found that spatial variations in coral cover were correlated with temperature variations on time scales of days to weeks. Shallow terrace and backreef sites with high coral cover (> 50%) had a highly variable temperature distributions, but their average weekly temperature distributions were lower and similar to offshore waters. The mechanism for maintaining this low weekly temperature was mean advection, which varied on a weekly timescale in response to wave forcing. Tides were also important in driving flow on the atoll, but their contribution to the net transport of heat was not significant. Wind and regional forcing were generally not important in driving flow inside the atoll. Buoyancy-driven flows were important within the lagoons, and in driving cross-shore exchange on forereef environments. The physical factors favoring high coral cover percentage varied according to the different prevailing hydrodynamic regimes: low temperatures in backreef habitats, short travel times in lagoon habitats (days since entering the reef system), and lower wave stress on forereef habitats. In light of future warming from climate change, local areas of reefs which maintain lower temperatures through wave-driven mean flows will have the best likelihood of promoting coral survival.