The temperature changes in the Southern Ocean have exhibited significant regional differences in response to climate change. In this study, observation, objective analysis, and reanalysis datasets are utilized to investigate temperature changes. The results show that there is an unexpected cooling trend reaching − 0.4 °C per decade, occurring in the South Pacific sector between 60°W and 180°. Whereas, there is also a significant warming occurring in the South Atlantic and Indian sectors, exhibiting an obvious zonal asymmetry of temperature trend within the Antarctic circumpolar current after 2005. This zonal asymmetry is primarily governed by ageostrophic advection changes, which are modulated by the combined effect of the zonal wind and the buoyancy fluxes. Cooling in the Pacific sector arises from both intensified westerly-driven cold water supply and enhanced buoyancy loss, and the latter is responsible for the significant deep cooling that penetrates the intermediate ocean. The net ageostrophic advection contributes − 148.7 TW to this cooling, which explains 75

The Alaskan North Slope (ANS) is a region of recurrent wind-driven upwelling, but the extent to which these events influence Beaufort Gyre (BG) variability and Arctic freshwater redistribution remains uncertain. We combine ERA5 winds, mooring velocity and hydrography, satellite dynamic ocean topography, SODA reanalysis, and idealized MITgcm experiments. During 2008–2020, 380 mooring-observed upwelling events were identified; 377 (99.2%) occurred under upwelling-favorable winds, and event-integrated wind forcing was correlated with observed upwelling intensity (r = 0.75). Monthly ANS upwelling activity was associated with enhanced DOT-derived BG strength during the Monthly ANS upwelling activity was significantly associated with enhanced DOT-derived BG strength during the event month after accounting for sea ice and the previous-month BG state; the lag-1 coefficient remained positive but was not statistically significant after accounting for sea ice. Upwelling also produced an immediate decrease in freshwater content on the shelf-ward side of the 1000-m isobath, while larger ANS freshwater losses preceded increased freshwater content in the adjacent southern-BG band after approximately 3–6 months. The observations and process model support a rapid geostrophic-adjustment pathway and a slower, spatially heterogeneous freshwater-redistribution pathway. In the passive-tracer experiment, 38.10% of the initially tagged shelf–slope halocline water crossed the 60-km slope-foot section within six days, and the velocity–tracer covariance accounted for 68.17% of the resolved cumulative transport. The result is interpreted as evidence for an eddy-related early-stage offshore pathway.

The westward expansion of the Beaufort Gyre (BG) is essential for the transport and redistribution of heat, freshwater, and nutrients in the western Arctic Ocean. During 2003–2014, the core and edge of BG expended westward significantly, as indicated by satellite dataset and reanalysis data. An idealized model with spatial and temporal variation of the anticyclonic surface stress also demonstrates the BG westward expansion. Based on the potential vorticity (PV) budget analysis of the idealized model results, the westward advection of thickness perturbation near the continental slope transports the negative PV anomalies generated by variations in surface stress, which contributes to the westward expansion of the BG. Idealized model case studies are conducted to investigate how displacement of surface stress field location, enlargement of surface stress field, and asymmetry enhancement of surface stress field affect the westward expansion and asymmetry of the BG via advective processes. The enlargement of surface stress led to the most significant enhancement in advection of thickness perturbation and a pronounced westward expansion of BG, with both the core and edge of BG westward expansion over 300 km. The asymmetry enhancement of surface stress significantly contributes to the pronounced zonal asymmetry of BG. Advection of thickness perturbation exerts a more pronounced influence on the western edge of BG, while advection of vorticity perturbation has a greater impact on the core of BG. The beta effect is essential for the westward expansion of the BG, a more pronounced beta effect leads to a more rapid westward expansion.

With global warming, the freshwater content in the Arctic Ocean has been steadily accumulating since the 21st century, which causes notable alterations in the export of freshwater from the Arctic Ocean. This paper presents a comparative analysis of the variations in liquid freshwater transport (FWT) through Fram Strait and Davis Strait, the primary export pathways of the Arctic freshwater, spanning from 1980 to 2023. We also use reanalysis data, combined with atmospheric and sea ice data, to explore the impact of atmospheric circulation anomaly and the distribution of freshwater content in the Arctic Ocean on FWT in the straits. The research findings reveal that over the past four decades, the FWT through the straits has not exhibited the anticipated continuous growth. Instead, we observed distinct temporal shifts in regional freshwater export patterns: The FWT in Fram Strait experienced significant increase prior to the 21st century (trend of 10.14 mSv/10yr during 1980-2000), whereas the FWT in Davis Strait showed acceleration after 2000 (trend of 13.69 mSv/10yr). There are significant interannual variations in the FWT in both straits, which are linked to the intensity of Atlantic inflow in the straits. Large scale circulation has a direct impact on FWT in straits, but there are significant regional differences. In the positive phase of the Arctic Oscillation (North Atlantic Oscillation) and the negative phase of the Dipole Anomaly, the cyclonic circulation anomaly in the Arctic Ocean favors enhanced surface outflow on both sides of Greenland. This, coupled with the storage of freshwater content in the margin of Greenland, leads to an intensification of the freshwater export through the Davis Strait. The FWT through the Fram Strait remains uncertain due to conflicting trends of increased outflow and decreased freshwater content. It can be determined that the FWT in Fram Strait is related to the upstream FWC, buffered by the accumulation of freshwater in northern Greenland. Furthermore, the ongoing Atlantic inflow warming against the backdrop of the Atlantic Multidecadal Oscillation phase transition results in sea ice melting in the Arctic Ocean in the long term, thereby increasing the freshwater content on both sides of Greenland and tending to boost the freshwater export through the straits.

Recent studies have reported that global upper ocean stratification has intensified under the influence of global warming. Nevertheless, using both observations and long-term reanalysis data, we find that concurrent with the significant ocean warming, the increasing trend of upper ocean stratification attenuated in the western tropical Pacific after 2000. This study highlights the effects of subsurface high spiciness (warm and salty) anomalies on the attenuation of the increasing stratification trend, which mirrors distinct vertical structures in the long-term changes in temperature and salinity. Subsurface warming, rather than sea surface warming, is the primary driver of the increase in the ocean heat content and the weakening of ocean stratification as it substantially reduces the magnitude of the trend in the vertical thermal density gradient after 2000. These phenomena are closely associated with processes on isopycnals and reflect ocean dynamics driven by large-scale atmospheric circulation. Intensified tropical trade winds and accelerated undercurrents facilitate the convergence of heat and salt in the western tropical Pacific. In addition, changes in the depth of the isopycnal layers induced by anomalous wind stress curl contribute to the subsurface spiciness variability through heaving. Notably, the consistent increase in the salinity from the surface to the subsurface also contributes to the post-2000 weakening trend of the vertical haline density gradient. Analysis within the isopycnal framework demonstrates that the emergence of subsurface salty water effectively offsets the negative contribution of the thermal component to the weakening of density stratification in relatively deeper layers.

The Antarctic Slope Current(ASC)links the processes occurring in the coast area with the global ocean by modulating the flow across the continental slope,which influences global overturning circulation and the mass balance of the Antarctic ice shelves.This paper aims to explore the effects of wind and buoyancy fluxes on the long-term changes in the ASC using observation and reanalysis datasets.From 1993 to 2022,the ASC accelerated in all seasons,particularly in austral autumn,and was accompanied with the advancement of the strong flow.The positive buoyancy flux anomaly generates a low-density anomaly,which is accumulated by the prevailing surface easterly,maintaining a sharp density front along the continental slope.The heat flux intensifies the positive trend of buoyancy flux in summer and autumn,increasing the input of the lighter density anomaly into the ocean and advancing the strong flow of ASC.Compared with the annual mean,the additional acceleration of the ASC in autumn is mainly due to the contribution of the barotropic component,which could be explained by the local momentum input from the weakly enhanced local surface wind.The acceleration of the ASC is primarily driven by the positive trend of the buoyancy flux,while the influence of the wind on its seasonal variability becomes more significant due to the contribution of the local surface wind in autumn.

Climate changes lead to significant warming of the Southern Ocean. By analyzing observational products and objective analysis data, this study reveals that the Antarctic Intermediate Water (AAIW) shows a zonal asymmetry of heat content changes, resulting from the different regional responses to the large-scale circulations. The heat content changes show significant interannual to decadal variations superimposed on a long-term trend, mainly attributed to the heat redistribution affected by the atmospheric circulations. AAIW in the Indian sector exhibits a significant widespread warming, and AAIW in the southwest Pacific sector presents an unexpected cooling. Warming has increased by 0.4 ZJ (zettajoules, 1 ZJ=1021 J) per decade since 1979 in the Indian sector, which is equivalent to the heat gain rate of 0.04 W/m2 during 1979-2019 in the Southern Ocean. Upwelling of warm circumpolar deep water driven by upward Ekman pumping, induced by the persistent positive phase of the Southern Annular Mode in recent years, plays a leading role in promoting this warming. The unexpected cooling in the southwest Pacific sector, reaching -0.2 ZJ per decade during 1979-2019, is due to the increasing cold water from sea ice and melting water. An increase of low-pressure anomaly facilitates the shallowing and tilting of isopycnals and the intrusion of cold water into the interior ocean, which is closely associated with the Atlantic multidecadal oscillation. The enhancement of this zonal asymmetry in the AAIW shows an increasing heat content in the Indian sector and a decreasing heat content in the Pacific sector, which implies that the Indian Ocean will become an important potential warming pool in the future.

The launch of the Soil Moisture and Ocean Salinity (SMOS) satellite has promoted research on sea surface salinity (SSS) and salinity fronts (SF). The SF in the central Pacific Ocean is influenced by El Niño and La Niña events, and the physical processes involved are complex. In this study, we evaluated the ability of the SMOS product from the Barcelona Expert Centre (BEC) to retrieve SF using a simple and intuitive method. Furthermore, this study investigated seasonal variations in the SF and its response to El Niño and La Niña events. The accuracy of the SMOS BEC L4 SSS is sufficient for studying SF. By selecting reasonable SF thresholds and analyzing its locations and intensities, in the central equatorial Pacific Ocean, SF can be divided into two: northern and southern SF. The variability in the northern SF is primarily influenced by the migration of the intertropical convergence zone (ITCZ), whereas both freshwater flux and salt advection are the primary factors in the southern SF. They correspond to El Niño and La Niña events through freshwater flux and salt advection. These findings can provide information for the study of the SF based on satellite data and enhance our understanding of El Niño Southern Oscillation (ENSO) dynamics.

The Beaufort Gyre is the largest freshwater reservoir in the Arctic Ocean. Long-term changes in freshwater reservoirs are critical for understanding the Arctic Ocean, and data from various sources, particularly observation or reanalysis data, must be used to the greatest extent possible. Over the past two decades, a large number of intensive field observations and ship surveys have been conducted in the western Arctic Ocean to obtain a large amount of CTD (Conductivity, Temperature, and Depth) data. Multi-machine learning methods were assessed and merged to reconstruct the annual salinity product in the Western Arctic Ocean over the period 2003-2022. Data mining-based machine learning methods reconstructed salinity product based on input variables determined by physical processes, such as sea level pressure, bathymetry, sea ice concentration, and sea ice drift. The root-mean-square error of sea surface salinity, in comparison to deep water, was effectively managed during machine learning, which exhibits higher sensitivity to variations in the atmosphere, sea ice, and ocean. The mean absolute errors in freshwater content and halocline depth within the Beaufort Gyre region for the salinity product from 2003 to 2022 are 0.98 m and 1.31 m, respectively, when compared to observational data. The salinity product provides reliable characterizations of freshwater content in the Beaufort Gyre and its variations at halocline depth. In polar regions where lacking observed data, we can build data mining-based machine learning methods to generate reliable data products to compensate for the inconvenience. Furthermore, the application potential of this multi-machine learning results approach for evaluating and integrating extends beyond the salinity field, encompassing hydrometeorology, sea ice thickness, polar biogeochemistry, and other related fields.

Analyses of vertically layered structures in ocean salinity present a recently amplified vertical contrast in the northwestern tropical Pacific, which has been attributed to the reversal of the long-term linear trend in salinity within the upper ocean from 1960 to 2023. Based on data obtained from both observations (Argo and WOD) and reanalysis (EN4), salinity trends shifted from freshening (− 0.04 psu/40 yr) to salinification (+ 0.04 psu/60 yr) in the near-surface (above 24.6 σ_θ surface), while subsurface (below 25 σ_θ surface) freshening further strengthened from – 0.03 psu/40 yr to – 0.1 psu/60 yr after 2000. The near-surface salinification can be partly explained by atmospheric forcing related to global warming. The anomalous cyclonic wind-induced Ekman suction and wind-driven horizontal salt transport were favorable for increased salinity in upper layers. Nevertheless, the oceanic dynamic forces governed the vertical salinity structure. Under a warming climate, heat influx and warm water accumulation due to diabatic effects play a deterministic role in isopycnal deepening. The changes in salinity evoked by isopycnal changes were investigated from two perspectives: entrainment at the bottom of 24.6 σ_θ layer and heaving variabilities for the upper layers above 24.6 σ_θ , were primary factors in near-surface salinification. However, the relative significance of heaving variabilities decreased with depth and the major controlling factor became contingent on spiciness variabilities. It is suggested that, owing to a northward migration of the outcrop line, subduction along the path of the geostrophic streamline from the ventilation region, where freshened spiciness anomalies can be injected into subduction surfaces, tended to dominate the significant freshening trend at subsurface isopycnals.

The increase in intense tropical cyclone (TC) activity across the western North Pacific (WNP) has often been attributed to a warming ocean. However, it is essential to recognize that the tropical WNP region already boasts high temperatures, and a marginal increase in oceanic warmth due to global warming does not exert a significant impact on the potential for TCs to intensify. Here we report that the weakened vertical wind shear is the primary driver behind the escalating trend in TC intensity within the summer monsoon trough of the tropical WNP, while local ocean surface and subsurface thermodynamic factors play a minor role. Through observational diagnoses and numerical simulations, we establish that this weakening of the vertical wind shear is very likely due to the increase in temperature of the Tibetan Plateau. With further warming of the Tibetan Plateau under the Representative Concentration Pathway 4.5 scenario, the projected TCs will likely become stronger.

Abstract. The global ocean has been warming significantly due to rapid climate change, leading to conspicuous changes in the subpolar Southern Ocean. Our study reveals that the heat exchange between Antarctic and subtropical oceans driven by wind, which plays an important role in modulating changes in regional ocean heat content (OHC) through meridional heat advections. In this study, we used the observed objective analysis and reanalysis datasets to explore the changes in subpolar ocean heat content and analyze attributions to the remarkable regional discrepancy. We found a notable difference in OHC trends between the Atlantic–Indian sector and the Pacific sector, which could be attributed to the inverse meridional heat advection caused by wind anomalies. Atlantic–Indian sector warming was significantly modulated by increasing meridional heat advection induced by the poleward westerly wind. In the Pacific sector, the enhanced wind resulted in substantial cold-water advection equatorward, causing significant cooling. These opposite advections are also occurring with the corresponding regional front movement, which also indicates the meridional heat exchange between oceans. This study highlights that wind anomalies play an important role in modulating the heat exchange between Antarctic and subtropical oceans. Consequently, the atmospheric forcing may become more significant to the heat redistribution in the Southern Ocean in the warmer future.

Against the background of wind-forcing change along with Arctic sea ice retreat, the mesoscale processes undergoing distinct variation in the Beaufort Gyre (BG) region are increasingly important to oceanic transport and energy cascades, and these changes subsequently put oceanic stratification into a new state. Here, the varying number and strength of eddies in the central Canada Basin (CB) and Chukchi–Beaufort continental slope are obtained based on mooring observations (2003–2018), altimetry measurements (1993–2019), and reanalysis data (1980–2020). In this paper, the variability in the BG halocline, representing the adjustment of stratification in the upper layer, is shown in order to analyse how variability occurs under changing mesoscale processes. We find that over almost the last 2 decades the halocline depth has deepened by ∼ 40 m in the south of the central gyre, while that in the north has deepened by ∼ 70 m according to multiple datasets. Surrounding the central gyre, the asymmetry of the halocline, with much steeper and deeper isopycnals over the southern continental slope, reduced after 2014. In the meantime, eddy activities in the upper layer from the southern margin of the BG to the abyssal plain have been enhanced. Moreover, the convergence of the eddy lateral flux has increased as the halocline structures on either side, which is at least 120 km from the central gyre, have reached a nearly identical and stable regime. It has been clarified that long-term dynamic eddy modulation through eddy fluxes, facilitating the freshwater redistribution, affects the meridional asymmetry of the BG halocline. Our results provide a better understanding of the eddy modulation processes and their influence on the halocline structure.

Extreme sea level events (ESLs) act as a comprehensive consequence of climate change, and a better understanding of the impact processes of climatic factors on ESLs variability is essential for obtaining a coastal sustainable development strategy. In this work, hourly sea-level data from 699 worldwide tide gauges between 1960 and 2013 were used to analyze the ESLs variability, and we selected 72 representative tide gauges in the Northwest Pacific, which stood out in terms of ESLs intensity, duration and occurrence. Under the climate change framework, The Northwest Pacific is a key area that subjected to stronger, longer, and more frequent ESLs after 1990, and reef coast ESLs gradually shifted their sensitivity from intensity to occurrence. TC-summer and winter are the peak seasons of ESLs during the year. The effects of water level discrepancy (WLD) on ESLs are increasing, and the growing impacts even exceeded the impact of sea-level at a few Indonesian tide gauges. Low frequency variations of sea-level are provided as the background of ESLs variabilities on a seasonal time scale and secular change, with more than 80% of tide gauges experiencing accelerated sea-level rise. In terms of magnitude, the high tide level is the major climatic factor to ESLs along the Northwest Pacific coast. The nested Gumbel–Hougaard copula function is built to evaluate the ESLs partial correlation-joint return period, which introduces the combined effect of WLD, sea-level variability, high tide level, and wind. Sea-level variability, WLD, and wind all shorten the ESLs joint return periods at more than 70% tide gauges, particularly, wind exhibits as a significant shortening climatic factor throughout the Northwest Pacific. Meanwhile, the high tide level shows significant and complicated contribution to the ESLs, which fluctuated according to the complex features of the tidal wave system, and this complexity makes it possible to increase the return period. An individual climatic factor influenced weakly on ESLs joint return period when a second climatic factor is introduced considering the interactions between different climatic factors. More tide gauges will likely exhibit complex features of the ESLs joint return period, and some tide gauges that have a shortened ESLs joint return period may even show an increase. Considering the coastal flooding risk framework, coastal flooding risk is growing in the decadal fluctuation, so the enhanced forecasting and prevention strategy against future ESLs will provide an effective blueprint for adaption and mitigation.

Ocean salinity can be used as an important indicator of climate change by measuring the global hydrological cycle. In our research, observations and reanalysis data sets are applied to determine that, from 1950 to 2018, long-term salinity change in the upper tropical Pacific Ocean was dominated by two empirical orthogonal function (EOF) leading modes on decadal to longer time scales. The first leading mode is defined as the decadal mode, which is related to the Interdecadal Pacific Oscillation (IPO). Additionally, the second leading mode is a global warming-related mode. The decadal mode is highly correlated with the IPO index and its decadal fluctuation significantly enhanced after the 1990s. Salinity budget analyses demonstrate that the freshwater flux term is the major contribution to decadal salinity change. We also proposed that the importance of ocean circulation modulation tends to be increasingly significant after the 1990s. The relative importance of the two salinity modes reversed over the upper 400 m. The global warming-related mode strengthened and became the dominant mode in the subsurface ocean, while the decadal mode weakened. The subsurface freshening is mainly induced by diapycnal mixing and the poleward migration of the ventilated region. Both of these processes were seen in subsurface isopycnal layers, which reveals a connection between ocean interior dynamic modulation and climate change.

海洋要素计算上机实验课是海洋科学专业本科生的一门专业必修实践课,针对该课程缺乏实验指导书的现状,对实验指导书的编写进行了研究.分析了指导书编写的必要性,并结合课程教学大纲要求,立足学生学习需求,重点阐述了指导书的编写构思,根据实践教学经验,从指导书的编写原则、框架内容设置及实验项目编排等方面进行了探讨,最后对新编指导书的应用情况及效果进行了简要论述.

随着北冰洋海冰快速减退,气-冰-海系统发生显著变化,波弗特流涡也发生显著变化.本文使用实测资料和海洋大气再分析数据,探讨北冰洋波弗特流涡的长期变化和大气动量输入对波弗特流涡变化的影响.波弗特流涡的长期变化可以分为3个典型时期(1980-1995年,1996-2007年,2008-2018年).最近时期(2008-2018年),波弗特流涡平均流涡强度达到4.39×10-7,相较于第1个时期(1980-1995年),流涡强度增加近2倍,达到稳定的状态.波弗特流涡范围扩大,主体向西北移动;上层海洋斜压性增强.与此同时,上层海洋环流主模态已发生显著转变:1980-1995年,环流主模态为影响整个加拿大海盆的加拿大海盆模态;2008-2018年的主模态则转变为影响整个研究海域的太平洋扇区模态.最近时期,表征气-海之间动量输入的气-海应力显著增加,尤其是夏末秋初的8-10月,与冰-海应力几乎相当.增加的大气动量输入带来平均动能增加,埃克曼泵压效应增强,下盐跃层深度加深,增加的大气动量输入进而导致近年来波弗特流涡的显著增强.加拿大海盆南部是大气动量输入的关键区.

Abstract The parasol effect of volcanic dust and aerosol caused by volcanic eruption results in the deepening and strengthening of the Arctic vortex system, thus stimulating or strengthening the Arctic Oscillation (AO). Three of the strongest AOs in more than a century have been linked to volcanic eruptions. Every significant fluctuation of the AO index (AOI) for many years has been associated with a volcanic eruption. Volcanic activity occurring at different locations in the Arctic vortex circulation will exert different effects on the polar vortex. Strong volcanic activity above level 5 erupting outside the Arctic vortex circulation can have a certain degree of influence on the Arctic oscillation and only cause small AOI fluctuations.

The parasol effect of volcanic dust and aerosol caused by volcanic eruption results in the deepening and strengthening of the Arctic vortex system, thus stimulating or strengthening the Arctic Oscillation (AO). Three of the strongest AOs in more than a century have been linked to volcanic eruptions. Every significant fluctuation of the AO index (AOI = ΔH_middle latitudes − ΔH_Arctic) for many years has been associated with a volcanic eruption. Volcanic activity occurring at different locations in the Arctic vortex circulation will exert different effects on the polar vortex.

Water cycle have prevailed on upper ocean salinity acting as the climate change fingerprint in the numerous observation and simulation works. Water mass in the Southern Ocean accounted for the increasing importance associated with the heat and salt exchanges between Subantarctic basins and tropical oceans. The circumpolar deep water (CDW), the most extensive water mass in the Southern Ocean, plays an indispensable role in the formation of Antarctic Bottom Water. In our study, the observed CTDs and reanalysis datasets are examined to figure out the recent salinity changes in the three basins around the Antarctica. Significant surface salinity anomalies occurred in the South Indian/Pacific sectors south of 60ºS since 2008, which are connected with the enhanced CDW incursion onto the Antarctic continental shelf. Saltier shelf water was found to expand northward from the Antarctica coast. Meanwhile, the freshening of Upper Circumpolar Deep Water(UCDW), salting and submergence of Subantarctic Mode Water(SAMW) were also clearly observed. The modified vertical salinity structures contributed to the deepen mixed layer and enhanced intermediate stratification between SAMW and UCDW. Their transport of salinity flux attributed to the upper ocean processes responding to the recent atmospheric circulation anomalies, such as the Antarctic Oscillation and Indian Ocean Dipole. The phenomena of SAMW and UCDW salinity anomalies illustrated the contemporaneous changes of the subtropical and polar oceans, which reflected the meridional circulation fluctuation. Salinity changes in upper southern ocean (< 2000m) revealed the influence of global water cycle changes, from the Antarctic to the tropical ocean, by delivering anomalies from high- and middle-latitudes to low-latitudes oceans.