SST Variability Research Articles

Climatic and human impact on the environment: Insight from the tetraether lipid temperature reconstruction in the Beibu Gulf, China

Organic proxies have been widely used to reconstruct temperature and terrestrial input variation at the interface between land and sea. However, the impact of human activities on these proxies has been little constrained, which might cause the misinterpretation of the sediment profile. In order to study the climatic and human impact on the environment, proxies in coastal regions, glycerol dialkyl glycerol tetraethers (GDGTs) in a sediment core spanning 115 years was analyzed from Beibu Gulf, China. The results indicate that isoprenoid GDGTs in the Beibu Gulf were mainly derived from Thaumarchaeota and the branched GDGTs originated mainly from terrestrial soil bacteria. The TEX86 index was applied to reconstruct the temporal SST variation. The results show that variation of TEX86-derived SST is controlled mainly by East Asian Monsoon system and partly by ENSO events. The methylation index of branched tetraethers or the cyclization index of branched tetraethers (MBT/CBT) derived mean annual air temperature (MAAT) agreed with MAAT record at the Qinzhou Station before 1982 AD. However, the population growth and economic development after 1982 AD caused the reduction of terrestrial organic matter input and increase of nutrient, leading to the thriving of Thaumarchaeota and increasing of in situ branched GDGTs proportion, which created the scatter of the MBT/CBT-reconstructed MAAT after 1982 AD. Therefore, human influence on GDGT proxies can be constrained in this way to avoid misinterpretation of paleoclimate and paleoenvironment records.

Variabilidade Temporal das Concentrações de Clorofila -A e da Temperatura Superficial do Mar na Costa Central de Santa Catarina

O fenômeno das florações de algas é conhecido mundialmente devido aos impactos diretos na saúde dos ecossistemas aquáticos, nos recursos pesqueiros e aquícolas, nas atividades recreacionais e na saúde humana. O presente estudo avaliou o uso de sensores satelitais na quantificação dos parâmetros de temperatura superficial do mar (TSM) e concentração de clorofila-a na superfície do mar (Chl-a) na costa de Santa Catarina, durante o período entre 2002 e 2019, objetivando identificar a variabilidade temporal da TSM e da Chl-a a partir da decomposição das séries temporais em tendência, sazonalidade e resíduos. Para atingir este objetivo foram adquiridas estimativas de TSM e Chl-a oriundas dos sensores orbitais Moderate-Resolution Imaging Spectroradiometer (MODIS) a bordo dos satélites (Aqua e Terra) e Visible Infrared Imaging Radiometer Suite (VIIRS) a bordo dos satélites (SNPP e NOAA-20). Através da extração dos valores de TSM e Chl-a para um ponto ao largo da costa central de Santa Catarina foram geradas séries temporais para o período especificado e aplicada a metodologia de decomposição de séries temporais para identificar oscilações de baixa frequência. Foi possível identificar que os eventos com maior Chl-a estão relacionados com eventos com menores valores de TSM. As componentes encontradas poderão ser utilizadas para modelos preditivos auxiliando assim a minimizar os impactos associados às florações de algas.

Magnitude and Phase of Diurnal SST Variations in the ACCESS‐S1 Model During the Suppressed Phase of the MJOs

AbstractDiurnal variations of sea surface temperature (DV SST) can affect the heat and moisture fluxes at the air‐sea interface during the suppressed phase of the MJO, thereby conditioning a favorable atmosphere environment for the subsequent MJO active phase. In order to better understand the causes and impacts of DV SST, and the modeling requirements for faithfully simulating these processes, we explore the DV SST and their influences on the air‐sea fluxes during the suppressed phases of three MJO events using a global coupled model, ACCESS‐S1, which has a 1‐m vertical resolution near the ocean surface and coupling frequency of 1 hr. Compared with the MTSAT‐1R satellite SST measurements, ACCESS‐S1 is able to simulate the magnitude of the DV SST reliably but has a phase delay in simulated peak SST of ~3 hr. Imposing an instant vertical mixing in the upper 10 m in ACCESS‐S1 would suppress the DV SST by >1°K and decrease the peak (>30 W m−2) and daily averaged latent heat flux. On the other hand, changing the atmosphere‐ocean coupling frequency within several hours mostly affects the DV SST phase instead of magnitude. Extreme DV SST (>1°K) occurs only when ocean mixing layer depth = 1 m. It implies that vertical resolution of ≤1 m near the sea surface is important for the coupled models to simulate both the magnitude and phase of DV SST accurately and thereby the air‐sea heat fluxes in future model forecast of the MJO.

Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

AbstractA recent study has brought to light the co‐existence of two distinct Atlantic Equatorial Modes during negative phases of the Atlantic Multidecadal Variability: the Atlantic Niño and Horse‐Shoe (HS) mode. Nevertheless, the associated air‐sea interactions for HS mode have not been explored so far and the prevailing dynamic view of the Atlantic Niño has been questioned. Here, using a forced ocean model simulation, we find that for both modes, ocean dynamics is essential to explain the equatorial SST variations, while air‐sea fluxes control the off‐equatorial SST anomalies. Moreover, we demonstrate the key role played by ocean waves in shaping their distinct structure and timing. For the positive phase of both Atlantic Niño and HS, anomalous westerly winds trigger a set of equatorial downwelling Kelvin waves (KW) during spring‐summer. These dKWs deepen the thermocline, favouring the equatorial warming through vertical diffusion and horizontal advection. Remarkably, for the HS, an anomalous north‐equatorial wind stress curl excites an upwelling Rossby wave (RW), which propagates westward and is reflected at the western boundary becoming an equatorial upwelling KW. The uKW propagates to the east, activating the thermocline feedbacks responsible to cool the sea surface during summer months. This RW‐reflected mechanism acts as a negative feedback causing the early termination of the HS mode. Our results provide an improvement in the understanding of the TAV modes and emphasize the importance of ocean wave activity to modulate the equatorial SST variability. These findings could be very useful to improve the prediction of the Equatorial Modes.

The role of the Atlantic Multidecadal Oscillation precondition in the teleconnection of different El Niño‐Southern Oscillation types and impacts on the 15°N–15°S South American sector precipitation

AbstractThe Eastern Pacific (EP) and Central Pacific (CP) El Niño‐Southern Oscillation (ENSO) types and their impacts on the tropical North Atlantic (TNA) SST variability and 15°N–15°S South American precipitation during the warm and cold phases of the Atlantic Multidecadal Oscillation (WAMO and CAMO) were evaluated during the 1901–2012 period. The results show more frequent ENSO events during the CAMO. The El Niño (EN) (La Niña [LN]) events, regardless of type (EP or CP), during the WAMO (CAMO) were accompanied by a warming (cooling) in the TNA after its mature phases. In these cases, extratropical teleconnection patterns are established through variations in the Pacific/North America (PNA) teleconnection pattern and are accompanied by variations in the Walker circulation. For the EN (LN) in the CAMO (WAMO), the tropical teleconnections occur predominant, through the Walker cell and the zonal inter‐basin gradient, which is intensified due to the SST gradient between the eastern equatorial Pacific (non‐neutral anomalies) and the equatorial Atlantic (neutral anomalies). These circulation pattern changes affect the precipitation patterns in the 15°N–15°S South American sector during December–January–February (D(0)JF(+1)) and March–April–May (MAM(+1)). The EP EN (EPEN) events are associated with the intensification of the negative precipitation anomalies in northeastern Brazil (NEB) during the WAMO and in the central part of the Amazon during the CAMO. In the case of CP EN (CPEN) events, the greatest differences between the AMO phases occur during MAM(+1), with reverse sign anomalies over northwestern South America. In the case of LN events, the largest differences occur in NEB, with reduced rainfall in the WAMO, regardless of type EP or CP. The results presented here highlight the role of low frequency oscillations in defining the teleconnection patterns between tropical Pacific and Atlantic Oceans, not discussed previously.

POLA SPASIAL DAN TEMPORAL DAERAH PENANGKAPAN IKAN PELAGIS MENGGUNAKAN DATA OSEANOGRAFI DI PERAIRAN SUMATERA BARAT

Perairan Sumatera Barat merupakan salah satu perairan yang memiliki potensi sumberdaya ikan yang sangat besar. Aktivitas penangkapan ikan banyak dilakukan di dekat pantai dan alat tangkap yang digunakan untuk penangkapan ikan di perairan Sumatera Barat salah satunya adalah bagan. Penelitian ini bertujuan untuk mengetahui hubungan suhu permukaan laut dan konsentrasi klorofil-a dengan hasil tangkapan ikan pelagis di perairan Sumatera Barat. Data yang digunakan berupa data SPL dan klorofil-a dalam kurun waktu tahun 2014 – 2016. Variabilitas SPL dan klorofil-a dianalisis menggunakan metode Empirical Orthogonal Function (EOF). Penelitian ini menunjukkan mode EOF SPL memperlihatkan bahwa keseluruhan nilai kisaran SPL berada diatas rata-rata (anomali positif) dengan ragam total sebesar 81,24%, sedangkan klorofil-a memperlihatkan bahwa nilai keseluruhan variabilitas berada pada rata-rata (anomali negatif) ragam total sebesar 70,23 %. Hasil korelasi silang antara SPL dengan ikan pelagis terdapat jeda waktu 2,2 bulan berarti ikan pelagis mendahului SPL dan dominan terjadi pada periode 6 bulanan. Hubungan antara klorofil-a dengan ikan pelagis dominan pada periode 0,5 tahun yang menunjukkan terdapat jeda antara klorofil-a dengan hasil tangkapan ikan pelagis dengan jeda waktu 22 hari.

Holocene reef growth in the tropical southwestern Atlantic: Evidence for sea level and climate instability

The Holocene epoch offers a potential analogue for understanding future sea-level variability as both SST's and Global Mean Sea Levels (GMSL) were at times higher than observed today. However, GMSL can differ significantly from Relative Sea Level (RSL), even at far-field sites remote from margins of former ice sheets. Much of this spatial variability has been shown to be consistent with the predictions of glacial isostatic adjustment (GIA) models. Whilst it is generally accepted that RSL at far-field sites reached its maximum during the mid-Holocene, there have been many interpretations of sea level fall following the highstand from ∼6 ka. Here, we present a RSL history from several tectonically stable, far-field sites in eastern Brazil, derived from 17 microatoll and 45 fossil reef flat ages. Our results show evidence for two periods of RSL instability during the Holocene which differ from GIA predictions, including a hiatus in reef growth ∼3.7–2.5 ka. These results are broadly synchronous with several other locations in the Southern Hemisphere suggesting global rather than regional climatic forcing mechanisms are responsible. Variations in SST and southern hemisphere ice sheet dynamics are proposed as possible controlling mechanisms for the observed RSL oscillations beginning at ∼3.7 ka and 2 ka respectively. We suggest that these global processes combined with increased precipitation (and higher sediment flux) from several regional climatic forces created inhospitable conditions for reef growth, contributing to the observed hiatus and reduced reef flat accretion during the late Holocene (∼2 ka to present).

Is the boreal spring tropical Atlantic variability a precursor of the Equatorial Mode?

The Equatorial Mode (EM) governs the tropical Atlantic inter-annual variability during boreal summer. It has profound impacts on the climate of adjacent and remote areas. However, predicting the EM is one of the most challenging and intriguing issues for the scientific community. Recent studies have suggested a possible connection between the boreal spring Meridional Mode (MM) and the EM through ocean wave propagation. Here, we use a set of sensitivity experiments with a medium-resolution ocean model to determine the precursor role of a MM to create equatorial SST variability. Our results demonstrate that boreal summer equatorial SSTs following a MM, are subject to two counteracting effects: the local wind forcing and remotely-excited oceanic waves. For a positive MM, the anomalous easterly winds blowing along the equator, shallow the thermocline, cooling the sea surface via vertical diffusion and meridional advection. Anomalous wind curl excites a downwelling Rossby wave north of equator, which is reflected at the western boundary becoming an equatorial Kelvin wave (KW). This downwelling KW propagates eastward, deepening the thermocline and activating the thermocline feedbacks responsible for the equatorial warming. Moreover, the local wind forcing and RW-reflected mechanism have a significant and comparable impact on the equatorial SST variability. Changes in the intensity and persistence of these distinct forcings will determine the equatorial SST response during boreal summer. Our results give a step forward to the improvement of the EM predictability.

Role of Stochastic Atmospheric Forcing from the South and North Pacific in Tropical Pacific Decadal Variability

Abstract Stochastic variability of internal atmospheric modes, known as teleconnection patterns, drives large-scale patterns of low-frequency SST variability in the extratropics. To investigate how the decadal component of this stochastically driven variability in the South and North Pacific affects the tropical Pacific and contributes to the observed basinwide pattern of decadal variability, a suite of climate model experiments was conducted. In these experiments, the models are forced with constant surface heat flux anomalies associated with the decadal component of the dominant atmospheric modes, particularly the Pacific–South American (PSA) and North Pacific Oscillation (NPO) patterns. Both the PSA and NPO modes induce basinwide SST anomalies in the tropical Pacific and beyond that resemble the observed interdecadal Pacific oscillation. The subtropical SST anomalies forced by the PSA and NPO modes propagate to the equatorial Pacific mainly through the wind–evaporation–SST feedback. This atmospheric bridge is stronger from the South Pacific than the North Pacific due to the northward displacement of the intertropical convergence zone and the associated northward advection of momentum anomalies. The equatorial ocean dynamics is also more strongly influenced by atmospheric circulation changes induced by the PSA mode than the NPO mode. In the PSA experiment, persistent and zonally coherent wind stress curl anomalies over the South Pacific affect the zonal mean depth of the equatorial thermocline and weaken the equatorial SST anomalies resulting from the atmospheric bridge. This oceanic adjustment serves as a delayed negative feedback and may be important for setting the time scales of tropical Pacific decadal variability.

Disentangling the Changes in the Indian Ocean Dipole–Related SST and Rainfall Variability under Global Warming in CMIP5 Models

AbstractThis study disentangles the changes in Indian Ocean (IO) dipole (IOD)-related SST and rainfall variability under global warming projected by the RCP8.5 runs in 29 CMIP5 models. The IOD rainfall changes consist of the thermodynamic component due to the surface moisture increase and the dynamic component due to the changes in IOD-related circulation. The IOD circulation changes are dominated by the IOD SST changes, which were further clarified using the amplitude and structural decomposition. The amplitudes of IOD SST and circulation are both decreased at rates of around 7.2% and 13.7% °C−1, respectively. The structural changes in IOD SST and circulation show a pattern with increases from the eastern to the western coast of the equatorial IO, similar to the pattern of so-called extreme IOD events in previous studies. Disentangling previous mechanisms and projections, we conclude that the increased atmospheric stability suppresses the amplitudes in IOD SST and circulation, whereas the positive IOD (pIOD)-like mean-state SST changes, leading to greater warming in the west than the east, mainly alter the structure of IOD SST and circulation. Both the amplitude and structural changes in the IOD SST and circulation are robust among the CMIP5 models, but their distinct patterns and out-of-step changes lead to an uncertain projection of IOD changes defined by the dipole mode index or EOF analysis in previous studies. Furthermore, the structural changes, dominated by the pIOD-like mean-state SST changes, are significantly correlated with the historical IOD amplitude among the models. Considering the commonly overestimated IOD amplitude as an emergent constraint, the structural changes in IOD SST and circulation should not be as robust as the original multimodel projection.

Detecting Change in the Indonesian Seas

1. Introduction The Indonesian seas play a fundamental role in the coupled ocean and climate system with the Indonesian Throughflow (ITF) providing the only tropical pathway connecting the global oceans. Pacific warm pool waters passing through the Indonesian seas are cooled and freshened by strong air-sea fluxes and mixing from internal tides to form a unique water mass that can be tracked across the Indian Ocean basin and beyond. The Indonesian seas lie at the climatological center of the atmospheric deep convection associated with the ascending branch of the Walker Circulation. Regional SST variations cause changes in the surface winds that can shift the center of atmospheric deep convection, subsequently altering the precipitation and ocean circulation patterns within the entire Indo-Pacific region. Recent multi-decadal changes in the wind and buoyancy forcing over the tropical Indo-Pacific have directly affected the vertical profile, strength, and the heat and freshwater transports of the ITF. These changes influence the large-scale sea level, SST, precipitation and wind patterns. Observing long-term changes in mass, heat and freshwater within the Indonesian seas is central to understanding the variability and predictability of the global coupled climate system. Although substantial progress has been made over the past decade in measuring and modelling the physical and biogeochemical variability within the Indonesian seas, large uncertainties remain. A comprehensive strategy is needed for measuring the temporal and spatial scales of variability that govern the various water mass transport streams of the ITF, its connection with the circulation and heat and freshwater inventories and associated air-sea fluxes of the regional and global oceans. This white paper puts forward the design of an observational array using multi-platforms combined with high-resolution models aimed at increasing our quantitative understanding of water mass transformation rates and advection within the Indonesian seas and their impacts on the air-sea climate system.

Regional climate, primary productivity and fish biomass drive growth variation and population resilience in a small pelagic fish

Abstract Environmental change often combined with selective harvesting has profound and diverse impacts on marine fish populations. Unlocking the biological consequences of these effects on wild fish is notoriously challenging, especially in highly productive but naturally variable systems with uncertain futures such as Eastern Boundary current systems. Here, we developed otolith increment-based growth chronologies covering half a century (53 years) for a small pelagic fish (Atlantic horse mackerel, Trachurus trachurus) in the northern limb of the Canary current upwelling system. We used increasingly complex mixed-effects models to partition individually resolved growth variation among intrinsic (Age and Age-at-capture) and extrinsic (biotic and abiotic factors) sources in four complementary data sets: a general population chronology, and three chronologies derived from age groups that reflect ontogenetic habitat shifts. First, we investigated the timing and scale of growth phase shifts and assessed the effects of extrinsic factors on inter-annual growth variation. Second, we quantified among and within cohort growth variability over time. Our results provided strong evidence for inter-annual SST and primary productivity variation impacting on Atlantic horse mackerel growth. We also identified phase shifts in growth that point to larger ecosystem-wide changes (regime shifts), potentially driven by large-scale climatic indices, such as North Atlantic Oscillation and East Atlantic pattern. Cohort-dependent growth effects likely reflect persistent environmental influences and density dependence. Further, we found evidence for carryover effects in growth whereby a poor start in life tended to persist despite compensatory growth being observed in some individuals. We show how population productivity can be impacted by multiple, interacting environmental and biotic factors leading to potential ecosystem regime shifts. Such information is key to understand recruitment dynamics and population persistence, and will have important implications for fisheries management and to those seeking to understand the effects of large-scale climate change on marine productivity.

A Hybrid Coupled Ocean-Atmosphere Model and Its Simulation of ENSO and Atmospheric Responses

A new hybrid coupled model (HCM) is presented in this study, which consists of an intermediate tropical Pacific Ocean model and a global atmospheric general circulation model. The ocean component is the intermediate ocean model (IOM) of the intermediate coupled model (ICM) used at the Institute of Oceanology, Chinese Academy of Sciences (IOCAS). The atmospheric component is ECHAM5, the fifth version of the Max Planck Institute for Meteorology atmospheric general circulation model. The HCM integrates its atmospheric and oceanic components by using an anomaly coupling strategy. A 100-year simulation has been made with the HCM and its simulation skills are evaluated, including the interannual variability of SST over the tropical Pacific and the ENSO-related responses of the global atmosphere. The model shows irregular occurrence of ENSO events with a spectral range between two and five years. The amplitude and lifetime of ENSO events and the annual phase-locking of SST anomalies are also reproduced realistically. Despite the slightly stronger variance of SST anomalies over the central Pacific than observed in the HCM, the patterns of atmospheric anomalies related to ENSO, such as sea level pressure, temperature and precipitation, are in broad agreement with observations. Therefore, this model can not only simulate the ENSO variability, but also reproduce the global atmospheric variability associated with ENSO, thereby providing a useful modeling tool for ENSO studies. Further model applications of ENSO modulations by ocean-atmosphere processes, and of ENSO-related climate prediction, are also discussed.

Southern African summer-rainfall variability, and its teleconnections, on interannual to interdecadal timescales in CMIP5 models

This study provides the first assessment of CMIP5 model performances in simulating southern Africa (SA) rainfall variability in austral summer (Nov–Feb), and its teleconnections with large-scale climate variability at different timescales. Observed SA rainfall varies at three major timescales: interannual (2–8 years), quasi-decadal (8–13 years; QDV) and interdecadal (15–28 years; IDV). These rainfall fluctuations are, respectively, associated with El Nino Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO) and the Pacific Decadal Oscillation (PDO), interacting with climate anomalies in the South Atlantic and South Indian Ocean. CMIP5 models produce their own variability, but perform better in simulating interannual rainfall variability, while QDV and IDV are largely underestimated. These limitations can be partly explained by spatial shifts in core regions of SA rainfall variability in the models. Most models reproduce the impact of La Nina on rainfall at the interannual scale in SA, in spite of limitations in the representation of ENSO. Realistic links between negative IPO are found in some models at the QDV scale, but very poor performances are found at the IDV scale. Strong limitations, i.e. loss or reversal of these teleconnections, are also noted in some simulations. Such model errors, however, do not systematically impact the skill of simulated rainfall variability. This is because biased SST variability in the South Atlantic and South Indian Oceans strongly impact model skills by modulating the impact of Pacific modes of variability. Using probabilistic multi-scale clustering, model uncertainties in SST variability are primarily driven by differences from one model to another, or comparable models (sharing similar physics), at the global scale. At the regional scale, i.e. SA rainfall variability and associated teleconnections, while differences in model physics remain a large source of uncertainty, the contribution of internal climate variability is increasing. This is particularly true at the QDV and IDV scales, where the individual simulations from the same model tend to differentiate, and the sampling error increase.

The Effect of the ENSO on the Variability of SST and Chlorophyll-a in the South China Sea

The South China Sea (SCS) is one of the western marginal oceans of the Pacific Ocean, surrounded by South China, the Indo Peninsula of China, Peninsular Malaysia, the Philippines, and Borneo Island. The effect of the ENSO on the Variability of SST and chlorophyll-a has been investigated by many researchers. However, in the study, there were not still a small number of researchers who studied in this SCS area using high-resolution satellite imagery data. Chlorophyll-a and SST data taken from MODIS data, and wind analysis data from CCMP (Cross Calibrate Multi-Platform). The results obtained, wind speed affects over changes SST and Chlorophyll-a at SCS. The influence of wind speed against the variability of SST is very strong, but otherwise, over variability of Chlorophyll-a is less impact. There is a high correlation between ENSO (El Nino) with the SST which tends to be dominant throughout the west season due to the influence of wind speed in the South China Sea from the Pacific towards Australia throughout the west season. However, this is in contrast to the correlation between ENSO and Chlorophyll-a which appears less dominant, which is suspected of other factors that may affect Chlorophyll-a anomalies in addition to wind and SST factors.

Unstable Little Ice Age climate revealed by high-resolution proxy records from northwestern China

Climatic instability, especially on decadal to multi-decadal time scales, has a profound impact on societal development and human welfare in semi-arid and arid regions. Previous work suggested that arid northwestern China was characterized by a dry Medieval Warm Period (MWP, from ca. 1000 to 1300 AD) and a wet Little Ice Age (LIA, from ca. 1400 to 1850 AD), but there is a lack of studies addressing the issue of climatic variability during the last millennium. Here, we present results from a diverse range of proxy records from northwestern China with the aim of evaluating the time variation of hydroclimatic variability during the MWP and LIA. Within the context of an overall cold climate, we detected a pattern of higher moisture variability during the LIA compared to the MWP. A comparison of the proxy records of climatic instability during the LIA from northwestern China with the major modes of SST and atmospheric variability, which affect moisture/precipitation in Asia, suggests that the instability of the North Atlantic Oscillation (NAO) from middle- to high-latitude regions during the LIA was a major driving factor. The westerlies may play an important role in linking the unstable climatic conditions observed in the above-mentioned regions. Our results support the concept that climatic instability was above the norm during cold periods, in contrast with present observations that demonstrate the occurrence of increasingly extreme climatic events with ongoing global warming.

Seasonal Antarctic pressure variability during the twentieth century from spatially complete reconstructions and CAM5 simulations

As most permanent observations in Antarctica started in the 1950s, understanding Antarctic climate variations throughout the twentieth century remains a challenge. To address this issue, the non-summer multi-decadal variability in pressure reconstructions poleward of 60°S is evaluated and assessed in conjunction with climate model simulations throughout the twentieth and early twenty-first centuries to understand historical atmospheric circulation variability over Antarctica. Austral autumn and winter seasons show broadly similar patterns, with negative anomalies in the early twentieth century (1905–1934), positive pressure anomalies in the middle twentieth century (1950–1980), and negative pressure anomalies in the most recent period (1984–2013), consistent with concurrent trends in the SAM index. In autumn, the anomalies are significant in the context of estimates of interannual variability and reconstruction uncertainty across most of the Antarctic continent, and the reconstructed patterns agree best with model-generated patterns when the simulation includes the forced response to tropical sea surface temperatures and external radiative forcing. In winter and spring, the reconstructed anomalies are less significant and are consistent with internal atmospheric variability alone. The specific role of tropical SST variability on pressure trends in these seasons is difficult to assess due to low reconstruction skill in the region of strongest tropical teleconnections, the large internal atmospheric variability, and uncertainty in the SST patterns themselves. Indirect estimates of pressure variability, whether through sea ice reconstructions, proxy records, or improved models and data assimilation schemes, will help to further constrain the magnitude of internal variability relative to the forced responses expected from SST trends and external radiative forcing.

Future evolution of Marine Heatwaves in the Mediterranean Sea

Extreme ocean warming events, known as marine heatwaves (MHWs), have been observed to perturb significantly marine ecosystems and fisheries around the world. Here, we propose a detection method for long-lasting and large-scale summer MHWs, using a local, climatological 99th percentile threshold, based on present-climate (1976–2005) daily SST. To assess their future evolution in the Mediterranean Sea we use, for the first time, a dedicated ensemble of fully-coupled Regional Climate System Models from the Med-CORDEX initiative and a multi-scenario approach. The models appear to simulate well MHW properties during historical period, despite biases in mean and extreme SST. In response to increasing greenhouse gas forcing, the events become stronger and more intense under RCP4.5 and RCP8.5 than RCP2.6. By 2100 and under RCP8.5, simulations project at least one long-lasting MHW every year, up to three months longer, about 4 times more intense and 42 times more severe than present-day events. They are expected to occur from June-October and to affect at peak the entire basin. Their evolution is found to occur mainly due to an increase in the mean SST, but increased daily SST variability also plays a noticeable role. Until the mid-21st century, MHW characteristics rise independently of the choice of the emission scenario, the influence of which becomes more evident by the end of the period. Further analysis reveals different climate change responses in certain configurations, more likely linked to their driving global climate model rather than to the individual model biases.

General seasonal phase-locking of variance and persistence: application to tropical pacific, north pacific and global ocean

A stochastic climate model is used to explain the major features of seasonal phase-locking of climate variability in general. The model is the classical damped persistence model, generalized with seasonal cycles in the growth rate and noise forcing. Our theory predicts distinct phase-locking features for different seasonal forcing. With seasonal growth rate, the forced variance lags the growth rate within a season, with the initial persistence in phase with the variance. With seasonal noise forcing, the variance also lags the noise forcing within a season, but the initial persistence lags the variance by a season. The theory is further applied successfully to the phase-locking of SST variability over the tropical Pacific, North Pacific and the world ocean. Overall, the variance and persistence is forced predominantly by the seasonal growth rate in the tropics with the variance and persistence in phase, but they are forced by the seasonal noise forcing in the mid-latitude with the variance and persistence in quadrature or even out phase. Our theory provides a general framework and a null hypothesis for the understanding of phase locking of climate variability in general.

Multi-trace-element sea surface temperature coral reconstruction for the southern Mozambique Channel reveals teleconnections with the tropical Atlantic

Abstract. Here we report seasonally resolved sea surface temperatures for the southern Mozambique Channel in the SW Indian Ocean based on multi-trace-element temperature proxy records preserved in two Porites sp. coral cores. Particularly, we assess the suitability of both separate and combined Sr∕Ca and Li∕Mg proxies for improved multielement SST reconstructions. Overall, geochemical records from Europa Island Porites sp. highlight the potential of Sr∕Ca and Li∕Mg ratios as high-resolution climate proxies but also show significant differences in their response at this Indian Ocean subtropical reef site. Our reconstruction from 1970 to 2013 using the Sr∕Ca SST proxy reveals a warming trend of 0.58±0.1 ∘C in close agreement with instrumental data (0.47±0.07 ∘C) over the last 42 years (1970–2013). In contrast, the Li∕Mg showed unrealistically large warming trends, most probably caused by uncertainties around different uptake mechanisms of the trace elements Li and Mg and uncertainties in their temperature calibration. In our study, Sr∕Ca is superior to Li∕Mg to quantify absolute SST and relative changes in SST. However, spatial correlations between the combined detrended Sr∕Ca and Li∕Mg proxies compared to instrumental SST at Europa revealed robust correlations with local climate variability in the Mozambique Channel and teleconnections to regions in the Indian Ocean and southeastern Pacific where surface wind variability appeared to dominate the underlying pattern of SST variability. The strongest correlation was found between our Europa SST reconstruction and instrumental SST records from the northern tropical Atlantic. Only a weak correlation was found with ENSO, with recent warm anomalies in the geochemical proxies coinciding with strong El Niño or La Niña. We identified the Pacific–North American (PNA) atmospheric pattern, which develops in the Pacific in response to ENSO, and the tropical North Atlantic SST as the most likely causes of the observed teleconnections with the Mozambique Channel SST at Europa.