Decadal Sea Surface Temperature Research Articles

Synchronous decadal climate variability in the tropical Central Pacific and tropical South Atlantic

Pantropical climate interactions across ocean basins operate on a wide range of timescales and can improve the accuracy of climate predictions. Here, we show in observations that Central Pacific (CP) El Niño-like sea surface temperature (SST) anomalies have coevolved with tropical South Atlantic SST anomalies on a quasi-decadal (~10-year) timescale over the past seven decades. During the austral autumn–winter season, decadal warm SSTs in the tropical CP effectively induce tropical SST cooling in the South Atlantic, mainly by strengthening the South Atlantic subtropical anticyclone via an extratropical atmospheric wave teleconnection in the southern hemisphere. Partially coupled pacemaker simulations corroborate the observational findings, indicating that tropical CP decadal SSTs play a primary pacing role, while Atlantic feedback is of secondary importance throughout the study period. Our results suggest that the tropical CP could be an important source of decadal predictability for tropical South Atlantic SST and the surrounding climate.

The role of the tropical Atlantic in tropical Pacific climate variability

Interactions between Atlantic and Pacific Oceans can affect tropical Pacific variability and its global impacts at both interannual and decadal timescales. Thus, a deepened understanding of the coupled Atlantic-Pacific interactions is needed. While possible dynamical mechanisms by which the Atlantic can influence the Pacific have been identified, the effectiveness of those mechanisms is difficult to establish using climate model simulations where Atlantic sea surface temperatures (SSTs) are prescribed and Pacific feedbacks cannot be realistically included. As an alternative approach, here we use a Linear Inverse Model (LIM) trained on observations and capable of correctly reproducing the observed statistics, to assess the relative role of the Atlantic-to-Pacific and Pacific-to-Atlantic influences on tropical Pacific variability. Our results indicate that Atlantic internal variability can enhance interannual SST anomalies in the eastern equatorial Pacific, and decadal SST anomalies in the central equatorial Pacific, while Pacific influences on the Atlantic significantly damp tropical Pacific decadal variability. This methodological framework could also be used to assess climate model fidelity in representing tropical basin interactions, helping to reconcile existing differences among models’ results.

Coastal Influence on Microbiomes of the Southwest Atlantic Ocean

The possible influence of the continent on the microbiome of the Southwest Atlantic Ocean (SAO) is not yet fully known. The aim of the present study was to evaluate the metagenomic diversity of the SAO nearshore in different locations (e.g., rivers and upwellings) and offshore locations. The studied sites (n=16) were clustered into four groups (G1-G4) according to the decadal sea surface temperature (SST) and levels of chlorophyll a (chl-a) (2007-2016). G1 (coastal upwelling) presented the highest chl-a values, G2 (shelf) had the highest SST, G3 (offshore north) had the lowest chl-a levels, and G4 (offshore south) was the coldest site. The higher nutrient levels may contribute to higher chl-a-based primary productivity and possibly higher bacterial productivity nearshore. The taxonomic and functional diversity of the total of 16 Illumina shotgun metagenomes were analysed (nearshore: 10, offshore: 6; mean ± standard deviation: 1.87±0.41 million reads per sample). The SAO microbiomes were split into two groups: nearshore and offshore. The SAO coastal zone had higher abundance of picoplanktonic cyanobacteria (e.g., Prochlorococcus), copiotrophic bacteria (e.g., Alteromonas), chl-a photosynthesis, and metabolism of nitrogen and phosphorus. In clear contrast with offshore microbiomes, nearshore microbiomes were heterogenous as a possible effect of riverine runoff and the upwelling. G1 microbiomes had higher abundance of copiotrophic bacteria, while G2 had a higher abundance of Prochlorococcus, and G3 had a higher abundance of Pelagibacter. Offshore metagenomes (G3 and G4) had enrichment of proteorhodopsin light harvesting and sulphur metabolism, possible relevant processes in the SAO. Metagenome assembled genomes (MAGs) demonstrated significant novel microbiome diversity. The most abundant MAGs belong to Flavobacteria and Euryarchaeota. The discrimination of microbial populations and metabolisms in the four studied oceanographic groups provides a first glimpse on the microbial landscape in the SAO.

Natural and Anthropogenic Climate Variability Signals in a 237‐Year‐Long Coral Record From the Philippines

AbstractBoth proxy and model studies conducted to understand anthropogenic warming have revealed historical variations in sea‐surface temperature (SST) since the industrial revolution. However, because of discrepancies between observations and models in the late nineteenth century, the timing and degree of anthropogenic warming remain unclear. In this study, we reconstructed a 237‐year‐long record of SST and salinity using a coral core collected from Bicol, southern Luzon, Philippines, which is located at the northern edge of the western Pacific warm pool. The SST record showed volcanic cooling after several volcanic eruptions, including the 1815 Tambora eruption, but the pattern of change differed. Decadal SST variations at Bicol are connected to Pacific Decadal Variability (PDV). Therefore, it is suggested that the PDV conditions at the time of the eruption may have influenced marine conditions, such as the degree and duration of cooling and/or salinity, after the eruptions. Although there were discrepancies in SST variations among the modeled, observed, and proxy SST data from the late nineteenth to early twentieth centuries, SST data from the late twentieth century showed globally coherent anthropogenic warming, especially after 1976. In particular, summer SST in the northwestern Pacific has become more sensitive to anthropogenic forcing since 1976.

Influence of the Northwest Pacific tripole mode on the mid-summer precipitation in North China and the regulation by the North Atlantic

The North China mid-summer (July) precipitation (NCJP) contributes the largest proportion of total annual precipitation in North China, with significant interdecadal and interannual variability. The interannual variability of the NCJP was further investigated on the basis of a study of its interdecadal variability and found that a sea surface temperature (SST) pattern in July located in the northwest Pacific, defined here as the northwest Pacific SST tripole (NWPT), can significantly influence the interannual variability of the NCJP, and that this relationship is regulated by the decadal northern North Atlantic SST (NNASST). Diagnostic analysis and the linear baroclinic model experiment indicate that the positive (negative) NWPT in July can excite an anomalous anticyclone (cyclone) in the region centered on the Korean peninsula and an anomalous cyclone (anticyclone) in the northwest Pacific off southeast Japan, thereby strengthening (weakening) the NCJP. When the decadal NNASST is in a significantly positive phase, the positive geopotential height anomalies it excites in the northwestern region off North China are not favorable for the connection between the NWPT and the NCJP. When the decadal NNASST is in a negative or insignificantly positive phase, the July NWPT and the NCJP have a significant positive correlation on interannual timescale.

Decadal variability of extreme high temperature in mid- and high-latitude Asia and its associated North Atlantic air–sea interaction

The decadal variability of extreme high temperature (EHT) in the mid and highlatitudes of continental Asia (MHLCA) and associated mechanisms were investigated. Observational analysis indicated that, after removing global warming, the first leading mode of the EHT events showed a meridional dipole pattern and had significant decadal variability. During the periods 1980–1994 and 2012–2019 (1995–2011), EHT events were more frequent and stronger (less frequent and weaker) in western-central Siberia than normal, whereas they were less frequent and weaker (more frequent and stronger) in the wide area to the south of Lake Baikal. Further Observational and CESM (Community Earth System Model) results based analysis suggested that decadal change in air–sea interaction in the North Atlantic play an important role in shaping the decadal variability of EHT events in MHLCA. On decadal timescales, meridional negative–positive–negative sea surface temperature (SST) anomalies in the North Atlantic and their coupled positive North Atlantic Oscillation can trigger stronger wave activity flux and cause a significant anticyclonic–cyclonic teleconnection wave train in the troposphere over the mid and high latitudes of the Eurasian continent. As a result, an anomalous high-pressure center is evident in western-central Siberia, and thereby reducing total cloud cover and causing stronger solar heating. Thus, EHT events become more frequent and stronger. On the contrary, for the areas south of Lake Baikal, EHT events are weakened by corresponding cyclonic circulation anomalies. Additionally, the CAM5 (Community Atmosphere Model version 5) experiments suggested more important driving role of the decadal North Atlantic tripole SST anomalies in the abovementioned processes.

Variability modes of September Arctic sea ice: drivers and their contributions to sea ice trend and extremes

The variability of September Arctic sea ice at interannual to multidecadal time scales in the midst of anthropogenically forced sea ice decline is not fully understood. Understanding Arctic sea ice variability at different time scales is crucial for better predicting future sea ice conditions and separating the externally forced signal from internal variability. Here, we study modes of variability, extreme events and trend in September Arctic sea ice in 100–150 year datasets by using time-frequency analysis. We extract the non-linear trend for sea ice area and provide an estimate for the sea ice loss driven by anthropogenic warming with a rate of ∼−0.25 million km2 per decade in the 1980s and accelerating to ∼−0.47 million km2 per decade in 2010s. Assuming the same accelerating rate for sea ice loss in the future and excluding the contributions of internal variability and feedbacks, a September ice-free Arctic could occur around 2060. Results also show that changes in sea ice due to internal variability can be almost as large as forced changes. We find dominant modes of sea ice variability with approximated periods of around 3, 6, 18, 27 and 55 years and show their contributions to sea ice variability and extremes. The main atmospheric and oceanic drivers of sea ice modes include the Arctic Oscillation and Arctic dipole anomaly for the 3 year mode, variability of sea surface temperature (SST) in the Gulf Stream region for the 6-year mode, decadal SST variability in the northern North Atlantic Ocean for the 18-year mode, Pacific Decadal Oscillation for the 27 year mode, and Atlantic Multidecadal Oscillation for the 55 year mode. Finally, our analysis suggests that over 70% of the sea ice area loss between the two extreme cases of 1996 (extreme high) and 2007 (extreme low) is caused by internal variability, with half of this variability being related to interdecadal modes.

Skillful decadal prediction skill over the Southern Ocean based on GFDL SPEAR Model-Analogs

The Model-Analogs technique is used in the present study to assess the decadal sea surface temperature (SST) prediction skill over the Southern Ocean (SO). The Model-Analogs here is based on reanalysis products and model control simulations that have ∼1° ocean/ice (refined to 0.5° at high latitudes) components and 100 km atmosphere/land components. It is found that the model analog hindcasts show comparable skills with the initialized retrospective decadal hindcasts south of 50°S, with even higher skills over the Weddell Sea at longer lead years. The high SST skills primarily arise from the successful capture of SO deep convection states. This deep ocean memory and the associated decadal predictability are also clearly seen when we assess the Model-Analogs technique in a perfect model context. Within 30°S–50°S latitudinal band, the model analog hindcasts show low skills. When we include the externally forced signals estimated from the large ensemble simulations, the model analog hindcasts and initialized decadal hindcasts show identical skills. The Model-Analogs method therefore provides a great baseline for developing future decadal forecast systems. It is unclear whether such analog techniques would also be successful with models that explicitly resolve ocean mesoscale eddies or other small-scale processes. This area of research needs to be explored further.

Long-Term Observations of Sea Surface Temperature Variability in the Gulf of Mannar

In this study, we conducted long-term temporal and spatial observations of monthly, interannual, and decadal sea surface temperature (SST) variation in the Gulf of Mannar (GoM) for the period from 1870 to 2018. We obtained climatological data from the Met Office Hadley Centre, UK. The monthly time series revealed that April and August were the warmest and coolest months of the year, respectively. The mean SSTs for April and August were 29.85 ± 0.44 °C and 27.15 ± 0.49 °C, respectively. The mean annual highest and lowest SSTs were observed in 2015 and 1890 with SSTs of 28.93 ± 0.31 °C and 27.45 ± 0.31 °C, respectively, and the annual time series revealed a warming SST trend of 0.004 °C. Decadal time series also revealed a warming SST trend of 0.04 °C, with the highest and lowest mean decadal SSTs being 28.56 ± 0.21 °C in 2010–2018 and 27.78 ± 0.25 °C in 1890–1889, respectively. Throughout the study period, the spatial distribution of climate trends over decades across the GoM revealed a strong spatial gradient, and the region between 6–8° N and 77–78° E was warmer than all other regions of the GoM.

Last Interglacial decadal sea surface temperature variability in the eastern Mediterranean

The Last Interglacial (~129,000–116,000 years ago) is the most recent geologic period with a warmer-than-present climate. Proxy-based temperature reconstructions from this interval can help contextualize natural climate variability in our currently warming world, especially if they can define changes on decadal timescales. Here, we established a ~4.800-year-long record of sea surface temperature (SST) variability from the eastern Mediterranean Sea at 1–4-year resolution by applying mass spectrometry imaging of long-chain alkenones to a finely laminated organic-matter-rich sapropel deposited during the Last Interglacial. We observe the highest amplitude of decadal variability in the early stage of sapropel deposition, plausibly due to reduced vertical mixing of the highly stratified water column. With the subsequent reorganization of oceanographic conditions in the later stage of sapropel deposition, when SST forcing resembled the modern situation, we observe that the maximum amplitude of reconstructed decadal variability did not exceed the range of the recent period of warming climate. The more gradual, centennial SST trends reveal that the maximal centennial scale SST increase in our Last Interglacial record is below the projected temperature warming in the twenty-first century.

Reconciling Roles of External Forcing and Internal Variability in Indian Ocean Decadal Variability Since 1920

AbstractOn decadal time scales, Indian Ocean sea surface temperatures (SSTs) exhibit coherent basin‐wide changes, but their origins are not well understood. Here we analyze observations and model simulations from Coupled Model Intercomparison Project Phase 6 and Community Earth System Model Version 1 to quantify the roles of external forcing and internal climate variability in causing Indian Ocean decadal SST variations. Results show that both external forcing and internal variability since 1920 have contributed to the observed decadal variations in linearly detrended Indian Ocean SSTs, and they exhibit an out‐of‐phase relationship since the 1950s. The internally‐generated variations arise from remote influences from the tropical Pacific and possible contributions from internal local processes, while the influence from the Atlantic Multidecadal Oscillation is opposite to that of the Interdecadal Pacific Oscillation. Decadal SST changes caused by nonlinear variations in greenhouse gases and aerosols are roughly out‐of‐phase with the internal variability, thus dampening observed SST variations since the 1950s.

The pacific decadal precession and its relationship to tropical pacific decadal variability in CMIP6 models

Persistent, multi-year shifts in atmospheric circulations and their associated influence on regional climates have profound impacts on physical, biological, and socioeconomic systems. The Pacific Decadal Precession (PDP), an atmospheric mode of variability consisting of a lower tropospheric height dipole which rotates counterclockwise over several years in the North Pacific, describes a series of such shifts in atmospheric circulations. One phase of the PDP, the north-south (N-S) phase, is hypothesized to be partially driven by central tropical Pacific (CP) sea surface temperature (SST) variability, but robust assessment of this dynamical connection in climate models remains to be done. In this study, we investigate this hypothesis with analyses in both reanalysis and selected models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) archive. We show that the emergence of the N-S phase is both related to and influenced by tropical Pacific decadal SST variability, specifically variability associated with CP El Niño-Southern Oscillation (ENSO) events. When examining the pre-industrial runs of the CMIP6 models, we find that most models cannot recover the characteristic cyclonic precession of the dipoles of the PDP, instead featuring only amplitude and sign changes of the N-S phase, Moreover, the models do not replicate the dynamical connections between the tropical Pacific and this North Pacific mode of climate variability. Our results suggest that primary reasons for this inconsistency are that models inaccurately simulate both the SST pattern associated with the PDP, shared low-frequency power associated with CP ENSO events, and incorrect Rossby wavetrains emanating from the tropical Pacific into the North Pacific on quasi-decadal timescales. Taken together, our analyses offer another benchmark by which to test the fidelity of the climate model simulations in capturing Pacific decadal climate variability in order to improve decadal-to-centennial climate projections.

Mechanisms of Decadal North Atlantic Climate Variability and Implications for the Recent Cold Anomaly

AbstractDecadal sea surface temperature (SST) fluctuations in the North Atlantic Ocean influence climate over adjacent land areas and are a major source of skill in climate predictions. However, the mechanisms underlying decadal SST variability remain to be fully understood. This study isolates the mechanisms driving North Atlantic SST variability on decadal time scales using low-frequency component analysis, which identifies the spatial and temporal structure of low-frequency variability. Based on observations, large ensemble historical simulations, and preindustrial control simulations, we identify a decadal mode of atmosphere–ocean variability in the North Atlantic with a dominant time scale of 13–18 years. Large-scale atmospheric circulation anomalies drive SST anomalies both through contemporaneous air–sea heat fluxes and through delayed ocean circulation changes, the latter involving both the meridional overturning circulation and the horizontal gyre circulation. The decadal SST anomalies alter the atmospheric meridional temperature gradient, leading to a reversal of the initial atmospheric circulation anomaly. The time scale of variability is consistent with westward propagation of baroclinic Rossby waves across the subtropical North Atlantic. The temporal development and spatial pattern of observed decadal SST variability are consistent with the recent observed cooling in the subpolar North Atlantic. This suggests that the recent cold anomaly in the subpolar North Atlantic is, in part, a result of decadal SST variability.

The Observed Relationship between Pacific SST Variability and Hadley Cell Extent Trends in Reanalyses

AbstractReanalysis and other observationally based estimates suggest that the tropics have expanded more than simulated by coupled climate models with historical radiative forcing. Previous research has attempted to reconcile this discrepancy by using climate model simulations with constrained tropical Pacific sea surface temperatures (SSTs) to account for the role of internal variability. Here the relationships between Hadley cell extent and internal SST variability and long-term warming are analyzed using purely observational techniques. Using linearly independent components of SST variability with reanalysis datasets, the statistical relationship between Pacific variability and Hadley cell extent is quantified by time scale. There is a strong correlation between North Pacific decadal SST variability and Southern Hemisphere Hadley cell extent. Conversely, there is a weaker observed relation between El Niño–Southern Oscillation (ENSO) and Hadley cell extent when low-frequency variability is filtered out of the ENSO signal. The observed linear sensitivity of Hadley cell width to long-term warming agrees with coupled general circulation model experiments when accounting for uncertainties, and there is a statistically significant relationship between Northern Hemisphere Hadley cell extent and long-term warming during boreal autumn.

CMIP5-Based Projection of Decadal and Seasonal Sea Surface Temperature Variations in East China Shelf Seas

The East China Shelf Seas, comprising the Bohai Sea, the Yellow Sea, and the shelf region of East China Sea, play significant roles among the shelf seas of the Western North Pacific Ocean. The projection of sea surface temperature (SST) changes in these regions is a hot research topic in marine science. However, this is a very difficult task due to the lack of available long-term projection data. Recently, with the high development of simulation technology based on numerical models, the model intercomparison projects, e.g., Phase 5 of the Climate Model Intercomparison Project (CMIP5), have become important ways of understanding climate changes. CMIP5 provides multiple models that can be used to estimate SST changes by 2100 under different representative concentration pathways (RCPs). This paper developed a CMIP5-based SST investigation framework for the projection of decadal and seasonal variation of SST in East China Shelf Seas by 2100. Since the simulation results of CMIP5 models may have degrees of errors, this paper uses hydrological observation data from World Ocean Atlas 2018 (WOA18) for model validation and correction. This paper selects seven representative ones including ACCESS1.3, CCSM4, FIO-ESM, CESM1-CAM5, CMCC-CMS, NorESM1-ME, and Max Planck Institute Earth System Model of medium resolution (MPI-ESM-MR). The decadal and seasonal SST changes in the next 100 years (2030, 2060, 2090) are investigated by comparing with the present analysis in 2010. The experimental results demonstrate that SST will increase significantly by 2100: the decadal SST will increase by about 1.55 °C, while the seasonal SST will increase by 1.03–1.95 °C.

Pacific Decadal Oscillation-like variability at a millennial timescale during the Holocene

Sea surface temperatures (SSTs) in the North Pacific exert a great influence on global climate and ecosystem changes. The Pacific Decadal Oscillation (PDO) is the leading mode of decadal SST variability in the North Pacific. The PDO-like variability at a millennial timescale during the Holocene is still poorly understood. In this study, the millennial-scale PDO-like variability during the Holocene is explored using model–data comparisons. To reduce the uncertainties caused by differential age controls, this study reconstructs the Holocene PDO-like index using two types of published proxy records, including 1) east–west SST contrast in the extratropical North Pacific and 2) PDO-related precipitation anomalies in East Asia. These two reconstructions reveal coherent changes in the PDO-like pattern during the Holocene, showing positive phases at 10.4–8.5 ka BP and 3.5–3.0 ka BP, and negative phases at 8.5–3.5 ka BP and 3.0–0.2 ka BP. Climate simulations suggest that the millennial-scale PDO-like variability is predominantly controlled by orbital forcing during the Holocene, leading to a positive phase of the PDO-like regime during the early Holocene. The positive phase of the PDO-like regime between 3.5 and 3.0 ka BP was probably caused by the internal feedback of the climate system, which the climate simulations fail to capture.

Exploring North Atlantic and North Pacific Decadal Climate Prediction Using Self-Organizing Maps

AbstractDecadal climate prediction can provide invaluable information for decisions made by government agencies and industry. Modes of internal variability of the ocean play an important role in determining the climate on decadal time scales. This study explores the possibility of using self-organizing maps (SOMs) to identify decadal climate variability, measure theoretical decadal predictability, and conduct decadal predictions of internal climate variability within a long control simulation. SOM is applied to an 11-yr running-mean winter sea surface temperature (SST) in the North Pacific and North Atlantic Oceans within the Community Earth System Model 1850 preindustrial simulation to identify patterns of internal variability in SSTs. Transition probability tables are calculated to identify preferred paths through the SOM with time. Results show both persistence and preferred evolutions of SST depending on the initial SST pattern. This method also provides a measure of the predictability of these SST patterns, with the North Atlantic being predictable at longer lead times than the North Pacific. In addition, decadal SST predictions using persistence, a first-order Markov chain, and lagged transition probabilities are conducted. The lagged transition probability predictions have a reemergence of prediction skill around lag 15 for both domains. Although the prediction skill is very low, it does imply that the SOM has the ability to predict some aspects of the internal variability of the system beyond 10 years.

The Footprint of Atlantic Multidecadal Oscillation on the Intensity of Tropical Cyclones Over the Western North Pacific

Sea surface temperature (SST) over the western North Pacific (WNP) exhibits strong decadal to multidecadal variability and in this region, warm waters fuel the tropical cyclones (TCs). Observational records show pronounced decadal variations in WNP TC metrics during 1950–2018. Statistical analysis of the various TC metrics suggests that the annual average intensity of WNP TCs is closely linked to the AMO (r = 0.86 at decadal timescales, p < 0.05). Observations and coupled atmosphere-ocean simulations show that the decadal WNP SST variations regarded as the primary driver of TC intensity, are remotely controlled by the AMO. Corresponding to the WNP SST warming, the local SLP gets lower and the tropospheric air becomes warmer and moister, enhancing atmospheric instability and the generation of convective available potential energy. These favorable changes in the background environment provide more “fuel” to the development of deep convection and intensify the WNP TCs. The footprints of AMO in WNP SST and atmospheric states through trans-basin interaction eventually exert a significant impact on the TC intensity over the WNP region.

Opposing Trends of Winter Cold Extremes over Eastern Eurasia and North America under Recent Arctic Warming

Under recent Arctic warming, boreal winters have witnessed severe cold surges over both Eurasia and North America, bringing about serious social and economic impacts. Here, we investigated the changes in daily surface air temperature (SAT) variability during the rapid Arctic warming period of 1988/89–2015/16, and found the daily SAT variance, mainly contributed by the sub-seasonal component, shows an increasing and decreasing trend over eastern Eurasia and North America, respectively. Increasing cold extremes (defined as days with daily SAT anomalies below 1.5 standard deviations) dominated the increase of the daily SAT variability over eastern Eurasia, while decreasing cold extremes dominated the decrease of the daily SAT variability over North America. The circulation regime of cold extremes over eastern Eurasia (North America) is characterized by an enhanced high-pressure ridge over the Urals (Alaska) and surface Siberian (Canadian) high. The data analyses and model simulations show the recent strengthening of the high-pressure ridge over the Urals was associated with warming of the Barents–Kara seas in the Arctic region, while the high-pressure ridge over Alaska was influenced by the offset effect of Arctic warming over the East Siberian–Chukchi seas and the Pacific decadal oscillation (PDO)–like sea surface temperature (SST) anomalies over the North Pacific. The transition of the PDO-like SST anomalies from a positive to negative phase cancelled the impact of Arctic warming, reduced the occurrence of extreme cold days, and possibly resulted in the decreasing trend of daily SAT variability in North America. The multi-ensemble simulations of climate models confirmed the regional Arctic warming as the driver of the increasing SAT variance over eastern Eurasia and North America and the overwhelming effect of SST forcing on the decreasing SAT variance over North America. Therefore, the regional response of winter cold extremes at midlatitudes to the Arctic warming could be different due to the distinct impact of decadal SST anomalies.

Unconventional Sea Surface Temperature Regime Around Japan in the 2000s–2010s: Potential Influences on Major Fisheries Resources

Climate-change associated changes in oceanographic conditions, particularly sea surface temperatures (SSTs), have systematically affected many marine fisheries resources around Japan. The Pacific Decadal Oscillation (PDO) index is considered one of the most important climate indices for describing basin-scale SST variations in the North Pacific, which are closely related to decadal variations in fisheries resources. Time series of the PDO index has been used to conventionally classify decadal conditions of ocean and fisheries resources around Japan as either warming or cooling regimes. It is now clear that for the 2000s to the mid-2010s, mostly during the “global surface warming slowdown,” the SST regime around Japan was unconventional; despite the PDO index being in a negative phase, which normally corresponds to a warming regime around Japan, SSTs exhibited decadal cooling in some waters and seasons. SSTs in the western part of the North Pacific subtropical gyre gradually decreased, particularly in autumn–spring, whereas SSTs in the western subarctic gyre and the Sea of Okhotsk increased. Moreover, SSTs between the subtropical and subarctic waters around northern Japan exhibited seasonal contrasts that were decadally intensified through the combined effects of cooling in winter–spring and warming in summer–autumn. Some major marine fisheries resources around Japan showed decadal increases or decreases beginning in the mid-2000s, and appeared to respond to the unconventional SST changes in their early life stages. In this paper, we review atmosphere and ocean conditions around Japan in the 2000s–2010s in terms of global climate, present an overview of potential impacts of decadal SST trends on five major commercial fisheries resources (walleye pollock, chum salmon, Japanese sardine, Japanese anchovy, and Japanese flying squid), and raise awareness that an unconventional regime can appear transiently during a state of global warming.