Near-surface Temperature Maximum Research Articles

Suitable areas for temperate fruit trees in a Brazilian hotspot area: Changes driven by new IPCC scenarios

Chilling accumulation and sufficient water availability are mandatory requirements for most temperate fruit trees (TFT) productivity. Given the strong dependence of these crops on air temperature and water availability, it is imperative to analyze the impacts of climate change on TFT, especially in areas considered persistent climate change hotspots. This study analyzed the impacts of climate change on suitable areas for planting TFT in a Brazilian state considered a hotspot for future climate changes - Minas Gerais, using an Agroclimatic Zoning (AZ) method, and outlined adaptation measures for the sustainable cultivation of the main TFT under future climate scenarios. Daily near-surface air temperature (minimum and maximum) and precipitation data were used from 10 Earth System Models (ESMs) from the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP), which are derived from the Coupled Model Intercomparison Project Phase 6 (CMIP6), in two Shared Socioeconomic Pathways scenarios (SSP2–4.5 and SSP5–8.5). The AZ method was applied for the current climate simulations (1995–2014), as well as for projections by the near (2041–2060) and far future (2081 – 2100) climate conditions considering two base temperature values (Tb = 7ºC and 13ºC). Given intense and persistent increases in air temperature, water deficit, and reduced chilling accumulation, TFT plantations will be restricted and economically unfeasible for about 69% (SSP2.4–5) to 86% (SSP5.8–5) of Minas Gerais in the far future for both Tb values. Only ∼6% (near future) and ∼2% (far future) of the study area located in a small portion of the Southern region of Minas Gerais will be suitable for TFT plantations. However, the future of TFT plantations in places classified as regular will depend on adopting adaptation measures to reduce vulnerability to these crops, including low-chill genotypes selection, improvements in breeding programs, using strategies to break dormancy artificially, and intensifying irrigation with less water-demanding techniques.

Climate risks and vulnerabilities of the Arabica coffee in Brazil under current and future climates considering new CMIP6 models

The susceptibility to climate change concerns the coffee market worldwide due to possible severe productivity losses. Brazil is the world's largest Arabica coffee producer and has crops in regions considered persistent climate change hotspots. Our study analyzed risks, vulnerabilities, and susceptibilities to pests and diseases in these regions under current and future climates and outlined adaptive measures to reduce future vulnerabilities. Ten risk indicators based on Arabica coffee requirements were proposed: water supply (Iw), base (TIB) and maximum temperature stresses (TImax), which delimit the temperature range where Arabica coffee grows and productivity is penalized outside both ranges, frost stress (TIfrost), diseases such as rust (DIrust), brown eye spot (DIbrown), and Phoma leaf spot (DIphoma), pests such as coffee berry borer (PIberry), coffee leaf miner (PIminer), and yield loss due to water stress (Iyg). Daily near-surface air temperature (minimum, mean, and maximum), relative humidity, precipitation, and global solar radiation were used from 16 General Circulation Models (GCMs) from the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP), which are derived from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in three Shared Socioeconomic Pathways scenarios (SSP245, SSP370 and SSP585). All risk indicators were calculated for the current climate (1995–2014) and projected for the near (2041–2060), intermediate (2061–2080), and far future (2081–2100) in three SSPs and then classified into five risk classes (very low, low, moderate, high and very high). Our results indicated that due to increases in TImax and Iyg indicators, with high to very high risk in area and magnitude, Arabica coffee plantations will be negatively affected and economically unfeasible for about 35 % to 75 % of the studied area throughout the 21st century. Furthermore, the rust and the leaf miner will remain a concern in future climates due to increased temperatures and reduced relative humidity. The future of Arabica coffee crops in Brazil will depend on adopting effective adaptive measures and prudent agricultural strategies to address anticipated risks, including shifting crops to higher altitude areas, introducing more climate-resilient coffee cultivars/varieties, using agroforestry or intercropping systems, planting in closer spacing or higher density planting, and employing dripper or partial root-zone irrigation techniques.

A model for the Arctic mixed layer circulation under a summertime lead: implications for the near-surface temperature maximum formation

Abstract. Leads in sea ice cover have been studied extensively because of the climatic relevance of the intense ocean–atmosphere heat exchange that occurs during winter. Leads are also preferential locations of heat exchange and melting in early summer, but their oceanography and climate relevance, if any, remains largely unexplored during summertime. In particular, the development of a near-surface temperature maximum (NSTM) layer typically 10–30 m deep under different Arctic basins has been observationally related to the penetration of solar radiation through the leads. These observations reveal that the concatenation of calm and wind events in the leads could facilitate the development of the NSTM layer. Using numerical modeling and an idealized framework, this study investigates the formation of the NSTM layer under a summer lead exposed to a combination of calm and moderate wind periods. During the calm period, solar heat accumulates in the upper layers under the lead. Near-surface convection cells are generated daily, extending from the lead sides to its center. Convection cells affect the heat storage in the mixed layer under the lead and the adjacent ice cap. A subsequent wind event (and corresponding ice drift) mixes and spreads fresh and cold meltwater into the warm layers near the surface. Surface mixing results in temperatures in the near-surface layers that are lower than in the deeper layers, where the impact of the surface stresses is weaker. Additionally, the warm waters initially located under the lead surface stretch and spread horizontally. Thus, an NSTM layer is formed. The study analyzes the sensitivity of the depth and temperature of the NSTM layer to buoyancy forcing, wind intensity, ice drift, stratification, and lead geometry. Numerical results suggest that the NSTM layer appears with moderate wind and ice drift and disappears when the wind intensity is higher than 9 m s−1. Depending on the background stratification, the calm period reinforces or becomes critical in NSTM layer formation. According to the results, ice drift is key to the development of the NSTM layer.

The Sensitivity of Green-Up Dates to Different Temperature Parameters in the Mongolian Plateau Grasslands

The rise in global average surface temperature has promoted the advancement of spring vegetation phenology. However, the response of spring vegetation phenology to different temperature parameters varies. The Mongolian Plateau, one of the largest grasslands in the world, has green-up dates (GUDs) with unclear sensitivity to different temperature parameters. To address this issue, we investigated the responses of GUDs to different temperature parameters in the Mongolian Plateau grasslands. The results show that GUDs responded significantly differently to changes in near-surface temperature (TMP), near-surface temperature maximum (TMX), near-surface temperature minimum (TMN), and diurnal temperature range (DTR). GUDs advanced as TMP, TMX, and TMN increased, with TMN having a more significant effect, whereas increases in DTR inhibited the advancement of GUDs. GUDs were more sensitive to TMX and TMN than to TMP. The sensitivity of GUDs to DTR showed an increasing trend from 1982 to 2015 and showed this parameter’s great importance to GUDs. Our results also show that the spatial and temporal distributions of temperature sensitivity are only related to temperature conditions in climatic zones instead of whether they are arid.

Detecting the response characteristics and thresholds of grassland spring phenology to climatic factors in the Mongolian Plateau

Understanding the response characteristics and thresholds of grassland spring phenology (GSP) to different climatic factors in arid and semi-arid regions is of great significance to deal with global climate change. The Mongolian Plateau is one of the largest plateaus located in arid and semi-arid regions of eastern Asia, extremely sensitive to climate change. At present, the response characteristics and thresholds of the grassland spring phenology to climate factors in the Mongolian Plateau remain uncertain. Here, we used statistical analysis, random forest and geographical detector to explore these uncertainty. We found that 1) 76.67% of study area showed a significant advancing trend. GSP has significantly advanced by −0.656 days/decade (P < 0.05) over the past three decades. 2) The vapor pressure (VAP) shows a more important impact on the GSP than other climate factors both in strength and range. Especially when the VAP value was between 2 and 5 hPa, the GSP advanced as the VAP increased. The near-surface temperature minimum (TMN), near-surface temperature (TMP), near-surface temperature maximum (TMX) and diurnal temperature range (DTR) have the greatest impact on the GSP in June, and the six-month cumulative effects of precipitation (PRE), wet day frequency (WET) and cloud cover (CLD) are greater than those in a single month. The interaction between VAP and PRE could largely explain GSP changes (69.35%). 3) The GSP have different response threshold to climate factors. The GSP advances as the temperature increases when TMP < 0 °C, DTR < 14 °C, TMX > 10 °C and TMN > −5 °C, and it delays as the FRS, WET and CLD increase. This study is of great significance to reveal the impact characteristics and threshold of climate change on the GSP, which could do help in understanding climate change.

Decadal scale trends in temperature, salinity, and sound speed in the Beaufort Sea since 1976

Profiles of conductivity and temperature as a function of depth (CTD) were collected in the Beaufort Sea during two U.S. Navy Ice Exercises in 2016, 2018, and 2020 (ICEXYY) in the month of March. The data show a significant departure from climatological values and significant variance at the interface between the Arctic Surface Layer (ASL) and the underlying Pacific Summer Water (PSW). Comparisons to older ICEX data collected over a 45 year period and to ice-tethered profiler (ITP) data since 2007 confirm both the subsurface warming trend and the variance at the ASL-PSW interface. Statistical analysis reveals a 0.4 degreeCelsius per decade increase in the near-surface temperature maximum (NSTM) near 75 m, which establishes two persistent acoustic propagation features beginning in the year 2000—a near-surface acoustic duct above 50 m and a subsurface acoustic duct, known as the Beaufort Lens, centered on 150 m water depth.

Prospects for acoustic remote sensing and acoustic system performance in the Beaufort Gyre region

In the Beaufort Gyre region north of Alaska, the vertical interleaving of the near-surface temperature maximum, the warm Pacific Summer Water (PSW), the cool Pacific Winter Water, and the Atlantic layer make for unusual acoustic conditions. The dynamics of these upper ocean layers cause typical complex and turbulent-like oceanic flow that causes geographically variable heat content and acoustics. A sound duct in the PWW, below the PSW and above the Atlantic Layer, filling ∼75 to 225 m depth, is prominent but not universal. Erosion of the PSW warm layer by either vertical or horizontal mixing processes often breaks the duct, with an additional seasonal cycle of ducting effectiveness, and allows sound to escape to interact with the scattering and attenuating surface. The duct enables communication and navigation signaling, but with that interruption caveat. It also allows passive sensing, best for sound that enters the duct and moves through it. A challenge is to utilize sound that exists outside the duct. This includes sounds emitted outside the duct by mammals, fracturing ice, or anything else. This sound will either cycle through the duct at steep angle, or stay above the duct and repeatedly reflect from the top boundary. The combination of unducted sound being subject to strong attenuation by ice or wave interaction (the typical high-latitude situation) and high variability of the duct effectiveness, imposes limitations on the usefulness of the otherwise convenient duct.

Estimation of Oceanic Heat Flux Under Sea Ice in the Arctic Ocean

Oceanic heat flux (Fw) is the vertical heat flux that is transmitted to the base of sea ice. It is the main source of sea ice bottom melting. The residual method was adopted to study oceanic heat flux under sea ice. The data acquired by 28 ice mass balance buoys (IMBs) deployed over the period of 2004 to 2013 in the Arctic Ocean were used. Fw values presented striking seasonal and spatial variations. The average summer Fw values for the Canada Basin, Transpolar Drift, and Multiyear Ice area were 16.8, 7.7, and 5.9 Wm−2, respectively. The mean summer Fw for the whole Arctic was 10.1 Wm−2, which was equivalent to a bottom melt of 0.4m. Fw showed an autumn peak in November in the presence of the near-surface temperature maximum (NSTM). The average Fw for October to December was 3.7Wm−2. And the average Fw for January to March was 1.0Wm−2, which was approximately one third of the average Fw in the presence of NSTM. The summer Fw was almost wholly attributed to the incident solar radiation that enters the upper ocean through leads and the open water. Fw calculated through the residual method using IMB data was compared with that calculated through the parameterization method using Autonomous Ocean Flux Buoy data. The results revealed that the Fw provided by the two methods were consistent when the sea ice concentration exceeded 70% and mixing layer temperature departure from freezing point was less than 0.15℃. Otherwise, the Fw yielded by the residual method was approximately one third smaller than that provided by the parameterization method.

Decadal variance of summer near-surface temperature maximum in Canada Basin of Arctic Ocean

In the summer Arctic, bump-like vertical temperature profiles of the upper layer in the Canada Basin suggest a near-surface temperature maximum (NSTM) beneath the mixed layer. This paper concentrates on describing the decadal variance of these NSTMs. Essentially, the temporal evolution of the summer NSTM revealed three decadal phases. The first period is before 2003, when the summer NSTM could rarely be observed except around the marginal of the Canada Basin. The second period is between 2003 and 2015, when the summer NSTM nearly occurred over the whole basin as accelerated decline of summer sea ice. The third period is from 2016 to 2017, when the summer NSTM almost disappeared due to prevailing warm surface water. Furthermore, for the background behind the decadal variance of summer NSTM, linear trends of the September minimum sea ice extent and surface water heat content in the Canada Basin from 2003 to 2017 were –2.75 ± 1.08 × 104 km2yr−1 and 2.29 ± 1.36 MJ m−2yr−1, respectively. According to a previous theory, if we assume that the trend of the summer surface water heat content was only contributed by NSTM, it would cause a decrease in sea ice thickness of approximately 13 cm. The analysis partially explains the reason for sea ice decline in recent years.

The importance of capturing late melt season sea ice conditions for modeling the western Arctic ocean boundary layer

To better understand the response of the western Arctic upper ocean to late summer ice-ocean interactions, a range of surface, interior, and basal sea ice conditions were simulated in a 1-D turbulent boundary layer model. In-ice and under-ice autonomous observations from the 2014 Marginal Ice Zone Experiment provided a complete characterization of the late melt-season sea ice and were used to set initial conditions, update boundary conditions, and conduct model validation studies. Results show that underestimates of open water and melt pond fraction at the sea ice surface had the largest influence on ocean-to-ice turbulent heat fluxes reducing basal melt rates by as much as 32%. This substantial reduction in latent heat loss was attributed to underestimates of open water areas and the exclusion of melt ponds by low-resolution synthetic aperture radar imagery. However, the greatest overall effect on the ice-ocean boundary layer came from mischaracterizations of basal roughness, with smooth ice scenarios resulting in 7 m of summer halocline shoaling and preservation of the near-surface temperature maximum. Rough ice conditions showed a 23% deepening of the mixed layer and erosion of heat storage above 40 m. Adjustments of conductive heat fluxes had little effect on the near-interface heat budget due to small internal thermal gradients within the late summer sea ice. Results from the 1-D boundary layer simulations highlight the most influential components of sea ice structure during late summer conditions and provide the magnitude of errors expected when ice conditions are mischaracterized.

Nanosecond laser ablation of target Al in a gaseous medium: explosive boiling

An approximate mathematical description of the processes of homogeneous nucleation and homogeneous evaporation (explosive boiling) of a metal target (Al) under the influence of ns laser radiation is proposed in the framework of the hydrodynamic model. Within the continuum approach, a multi-phase, multi-front hydrodynamic model and a computational algorithm are designed to simulate nanosecond laser ablation of the metal targets immersed in gaseous media. The proposed approach is intended for modeling and detailed analysis of the mechanisms of heterogeneous and homogeneous evaporation and their interaction with each other. It is shown that the proposed model and computational algorithm allow modeling of interrelated mechanisms of heterogeneous and homogeneous evaporation of metals, manifested in the form of pulsating explosive boiling. Modeling has shown that explosive evaporation in metals is due to the presence of a near-surface temperature maximum. It has been established that in nanosecond pulsed laser ablation, such exposure regimes can be implemented in which phase explosion is the main mechanism of material removal.

Large Eddy Simulation of Heat Entrainment Under Arctic Sea Ice

AbstractArctic sea ice has declined rapidly in recent decades. The faster than projected retreat suggests that free‐running large‐scale climate models may not be accurately representing some key processes. The small‐scale turbulent entrainment of heat from the mixed layer could be one such process. To better understand this mechanism, we model the Arctic Ocean's Canada Basin, which is characterized by a perennial anomalously warm Pacific Summer Water (PSW) layer residing at the base of the mixed layer and a summertime Near‐Surface Temperature Maximum (NSTM) within the mixed layer trapping heat from solar radiation. We use large eddy simulation (LES) to investigate heat entrainment for different ice‐drift velocities and different initial temperature profiles. The value of LES is that the resolved turbulent fluxes are greater than the subgrid‐scale fluxes for most of our parameter space. The results show that the presence of the NSTM enhances heat entrainment from the mixed layer. Additionally there is no PSW heat entrained under the parameter space considered. We propose a scaling law for the ocean‐to‐ice heat flux which depends on the initial temperature anomaly in the NSTM layer and the ice‐drift velocity. A case study of “The Great Arctic Cyclone of 2012” gives a turbulent heat flux from the mixed layer that is approximately 70% of the total ocean‐to‐ice heat flux estimated from the PIOMAS model often used for short‐term predictions. Present results highlight the need for large‐scale climate models to account for the NSTM layer.

Field observations and results of a 1-D boundary layer model for developing near-surface temperature maxima in the Western Arctic

Summer sea ice extent in the Western Arctic has decreased significantly in recent years resulting in increased solar input into the upper ocean. Here, a comprehensive set of in situshipboard, on-ice, and autonomous ice-ocean measurements were made of the early stages of formation of the near-surface temperature maximum (NSTM) in the Canada Basin. These observations along with the results from a 1-D turbulent boundary layer model indicate that heat storage associated with NSTM formation is largely due to the absorption of penetrating solar radiation just below a protective summer halocline. The depth of the summer halocline was found to be the most important factor for determining the amount of solar radiation absorbed in the NSTM layer, while halocline strength controlled the amount of heat removed from the NSTM by turbulent transport. Observations using the Naval Postgraduate School Turbulence Frame show that the NSTM was able to persist despite periods of intermittent turbulence because transport rates were too small to remove significant amounts of heat from the NSTM layer. The development of the early and late summer halocline and NSTM were found to be linked to summer season buoyancy and wind events. For the early summer NSTM, 1-D boundary layer model results show that melt pond drainage provides sufficient buoyancy to the summer halocline to prevent subsequent wind events from mixing out the NSTM. For the late summer NSTM,limited freshwater inputs reduce the strength of the summer halocline making the balance between interfacial stresses and buoyancy more tenuous. As a result, the late summer NSTM is an ephemeral feature dependent on local wind conditions, while the early summer NSTM is more persistent and able to store heat in the near-surface ocean beyond the summer season.

High-resolution daily gridded data sets of air temperature and wind speed for Europe

Abstract. New high-resolution data sets for near-surface daily air temperature (minimum, maximum and mean) and daily mean wind speed for Europe (the CORDEX domain) are provided for the period 2001–2010 for the purpose of regional model validation in the framework of DecReg, a sub-project of the German MiKlip project, which aims to develop decadal climate predictions. The main input data sources are SYNOP observations, partly supplemented by station data from the ECA&amp;amp;D data set (http://www.ecad.eu). These data are quality tested to eliminate erroneous data. By spatial interpolation of these station observations, grid data in a resolution of 0.044° (≈ 5km) on a rotated grid with virtual North Pole at 39.25° N, 162° W are derived. For temperature interpolation a modified version of a regression kriging method developed by Krähenmann et al.(2011) is used. At first, predictor fields of altitude, continentality and zonal mean temperature are used for a regression applied to monthly station data. The residuals of the monthly regression and the deviations of the daily data from the monthly averages are interpolated using simple kriging in a second and third step. For wind speed a new method based on the concept used for temperature was developed, involving predictor fields of exposure, roughness length, coastal distance and ERA-Interim reanalysis wind speed at 850 hPa. Interpolation uncertainty is estimated by means of the kriging variance and regression uncertainties. Furthermore, to assess the quality of the final daily grid data, cross validation is performed. Variance explained by the regression ranges from 70 to 90 % for monthly temperature and from 50 to 60 % for monthly wind speed. The resulting RMSE for the final daily grid data amounts to 1–2 K and 1–1.5 ms−1 (depending on season and parameter) for daily temperature parameters and daily mean wind speed, respectively. The data sets presented in this article are published at doi:10.5676/DWD_CDC/DECREG0110v2.

The impact of stored solar heat on Arctic sea ice growth

AbstractHigh‐resolution measurements of ocean temperature and salinity in the Arctic Ocean's Canada Basin reveal the importance of the release of solar‐derived stored ocean heat on sea ice growth. Locally absorbed summer solar heat is stored in a near‐surface temperature maximum (NSTM) layer underlying the mixed layer. The heat content of the NSTM layer was anomalously large following summer 2007, which saw considerable sea ice losses and intense solar absorption into the exposed surface ocean. Measurements provide evidence for the entrainment of NSTM layer heat in fall/winter 2007–2008 by shear‐driven mixing, and convective mixing by the release of dense, salty plumes during sea ice growth. While at least a portion of the NSTM layer was eroded, deeper warm ocean layers remained unaffected. It is shown that the release of solar heat stored following summer 2007 was sufficient to have reduced sea ice thickness at the end of the 2008 growth season by about 25%.

Large-scale temperature and salinity changes in the upper Canadian Basin of the Arctic Ocean at a time of a drastic Arctic Oscillation inversion

Abstract. Between 2008 and 2010, the Arctic Oscillation index over Arctic regions shifted from positive values corresponding to more cyclonic conditions prevailing during the 4th International Polar Year (IPY) period (2007–2008) to extremely negative values corresponding to strong anticyclonic conditions in 2010. In this context, we investigated the recent large-scale evolution of the upper western Arctic Ocean, based on temperature and salinity summertime observations collected during icebreaker campaigns and from ice-tethered profilers (ITPs) drifting across the region in 2008 and 2010. Particularly, we focused on (1) the freshwater content which was extensively studied during previous years, (2) the near-surface temperature maximum due to incoming solar radiation, and (3) the water masses advected from the Pacific Ocean into the Arctic Ocean. The observations revealed a freshwater content change in the Canadian Basin during this time period. South of 80° N, the freshwater content increased, while north of 80° N, less freshening occurred in 2010 compared to 2008. This was more likely due to the strong anticyclonicity characteristic of a low AO index mode that enhanced both a wind-generated Ekman pumping in the Beaufort Gyre and a possible diversion of the Siberian River runoff toward the Eurasian Basin at the same time. The near-surface temperature maximum due to incoming solar radiation was almost 1 °C colder in the southern Canada Basin (south of 75° N) in 2010 compared to 2008, which contrasted with the positive trend observed during previous years. This was more likely due to higher summer sea ice concentration in 2010 compared to 2008 in that region, and surface albedo feedback reflecting more sun radiation back in space. The Pacific water (PaW) was also subjected to strong spatial and temporal variability between 2008 and 2010. In the Canada Basin, both summer and winter PaW signatures were stronger between 75° N and 80° N. This was more likely due to a strong recirculation within the Beaufort Gyre. In contrast, south of 75° N, the cooling and warming of the summer and winter PaW, respectively, suggest that either the PaW was less present in 2010 than in 2008 in this region, and/or the PaW was older in 2010 than in 2008. In addition, in the vicinity of the Chukchi Sea, both summer and winter PaW were significantly warmer in 2010 than in 2008, as a consequence of a general warming trend of the PaW entering in the deep Arctic Ocean as of 2008.

Winter sea‐ice melt in the Canada Basin, Arctic Ocean

Recent warming and freshening of the Canada Basin has led to the year‐round storage of solar radiation as the near‐surface temperature maximum (NSTM). Using year‐round ocean (from ice tethered profilers and autonomous ocean flux buoys), sea‐ice (from ice mass balance buoys), and atmosphere (from NCEP/NCAR reanalysis) data from 2005–2010, we find that heat from the NSTM is entrained into the surface mixed layer (SML) during winter. Entrainment can only occur when the base of the SML reaches the top of the NSTM. If this condition is met, the surface forcing and stratification together determine whether the SML deepens into the NSTM. Heat transfer occurs by diffusion or by the erosion of the summer halocline. The average temperature of the SML warmed by as much as 0.06°C during storm events. Solar radiation began warming the SML about 1 month early during the winter of 2007–2008 and this can be explained by thin sea ice.

Variation of upper-ocean heat content in the Canada Basin in summers of 2003 and 2008

Conductivity, temperature, and depth data collected during the summers of 2003 and 2008 were usedto study upper-ocean (top 200 m) heat content in the Canada Basin. The variation of heat content with depth, heat content diFFErences between the summers, principal driving factors, and horizontal spatial scale diFFErenceswere analyzed. A catastrophic reduction of sea ice cover in the Canada Basin was evident in 2008 by comparisonwith 2003, suggesting that more solar radiation was absorbed in the upper ocean during the summer of 2008. Thesea ice reduction produced more freshwater in the upper ocean. Thus, seawater properties changed. The studyshows that the huge reduction of sea ice would result in two changes-widespread warming of the upper ocean, and the depth of pacific inflow water in the basin increased substantially. Near-surface temperature maximum(NSTM) water was also analyzed as an indicator of Arctic Ocean warming.

Modeling the formation and fate of the near‐surface temperature maximum in the Canadian Basin of the Arctic Ocean

A numerical model is used to investigate the time and space extent of the near‐surface temperature maximum (NSTM) of the Canadian Basin of the Arctic Ocean over the years 2000–2009. The NSTM is formed from local summertime absorption of solar radiation which, in some circumstances, descends through the fall and early winter to form a warm subsurface layer just below the winter mixed layer. We find that winter survival of this layer is confined largely to the Beaufort Gyre of the Canadian Basin, where Ekman convergence and downwelling push the summer warm layer down below the winter mixing depth. In recent years, summer stratification has increased, downwelling has accelerated, and the NSTM has warmed as the sea ice cover in the Beaufort Gyre has thinned. The result is a strengthening NSTM which contained enough heat by the end of winter 2007/2008 to melt about 20 cm of sea ice. Northwest of Alaska the model also simulates a second, deeper temperature maximum layer that forms from advection of saltier summer Pacific water. However, this layer is difficult to adequately resolve and maintain given the model's resolution.

Changes to the near-surface waters in the Canada Basin, Arctic Ocean from 1993–2009: A basin in transition

[1] Increased sea ice melt and decreased surface albedo have changed the near-surface water mass structure of the Canada Basin. From 1993–2009, the near-surface temperature maximum (NSTM) and remnant of the previous winter's mixed layer (rWML) warmed by about 1.5°C and 0.5°C and freshened by about 4 and 2 practical salinity units, respectively. Results from a 1-D model suggest rWML warming can be explained by heat diffusion from both the NSTM and Pacific Summer Water (PSW). The same model predicts salinization of the rWML, whereas freshening was observed. This suggests that changes to the rWML are from both diffusion and the accumulation of freshwater. The rWML's salinity was associated with distance from the center of the Beaufort Gyre; the rWML at stations inside the gyre was on average 1.9 salinity units fresher than at stations outside. In addition, the salinity of PSW in the Canada Basin - defined by its local temperature maximum - freshened from about 30–32 in 1993 to 28–32 in 2008. Order of magnitude calculations suggest that neither changes in PSW source waters nor changes in advection pathways of PSW explain this freshening. Our model suggests that salt diffused from PSW to the freshening rWML; this diffusion increased (and freshened the PSW salinity range) as the rWML freshened. These results show that surface effects through warming and ice melt are felt to at least the depth of PSW. Observations from 2009 show the appearance of a third temperature maximum from an as yet unknown source.