High Sea Surface Temperature Research Articles

Stable isotopic (δ18O and δ2H) and geospatial approach for evaluating extreme rainfall events

Natural disasters are more frequent in the tropical region in the recent past due to anthropogenic forcing and consequent climate change. In this context, understanding the genesis and pattern of extreme rainfall events are important to devise disaster management plans. Two natural disaster events, Cyclone Ockhi (05 December 2017) and a torrential rainfall event (944 mm in 24 h) occurred on 26 July 2005, that had caused large scale devastation, loss of lives and properties, in Mumbai, India were evaluated using stable isotopes (δ 18 O and δ 2 H) of precipitation and geospatial data. Both the events were analysed and compared to understand their occurrences, moisture source regions and deduce the atmospheric factors responsible for their formation. Distinctly depleted stable isotopic content in rains were observed during the Cyclone Ockhi, while, during the extreme rainfall event, it was same as that of the normal monsoon rains, which is attributed to the dynamic nature of the moisture. The depleted isotopic signature of the cyclone may be because of the isotopic fractionation effect caused by the organized convective condition and vapour recycling along the trajectory. The genesis, structure and pattern of both the extreme events were evaluated using Sea Surface Temperature (SST), Outgoing Longwave Radiation (OLR) and Relative Humidity (RH) data. Wind pattern and moisture transport pathways were derived using HYSPLIT backward trajectory model. Prevalence of high SST over the southwest Bay of Bengal and adjoining areas of Sri Lanka as well as in the Arabian Sea was responsible for the genesis and intensification of the Cyclone Ockhi. The extremely low OLR value indicated intense and deep convection over the region during the cyclone. The large scale altitudinal variation in RH created unstable condition in the troposphere, consequently, strengthened the cyclone. The intensive shallow convection, continuous supply of moisture from the Arabian Sea and the orographic uplifting of clouds at the Western Ghats were responsible for the occurrence of torrential rainfall on 26 July 2005 in Mumbai. The wind pattern during the cyclone was distinct; it was circular and ascending upward, while, it was more or less horizontal and was descending downwards during the torrential rainfall event. The atmospheric processes responsible for the occurrence of two natural disaster rain events were also conceptualized. Although, the isotope data is limited, the study is first of its kind and it provides better insights into the genesis, intensification of the extreme rainfall events that are essential for forecasting, planning disaster mitigation measures and in warning strategies of this region. • Genesis, structure and pattern of two natural disaster events (Cyclone Ockhi and a torrential rainfall) were evaluated. • The atmospheric processes responsible for the extreme events were conceptualized. • Prevalence of deep convection during Cyclone Ockhi and shallow convection during torrential rainfall event was deduced.

A Warming Mediterranean: 38 Years of Increasing Sea Surface Temperature

The Mediterranean basin has been classified as a hot-spot for climate change. The Mediterranean Sea plays a fundamental regulatory role in the regional climate. We have analyzed the largest available and complete time series (1982–2019) of blended sea surface temperature (SST) data to study its seasonal cycle and look for a possible warming trend in the basin. From the analysis of the Mediterranean mean SST time series, a new temporal seasonal division is derived that differs from the one used in atmospheric climatology. Then, the SST time series were decomposed into their seasonal and trend components, and a consistent warming trend of 0.035 °C/year was obtained. The nature of this trend has been investigated, indicating a higher warming trend for both maximum and high/summer SST values than for the winter/colder ones. This reinforces the consistency of the SST increase since it is not only based on the presence of extreme values, but on a homogeneous basin global increase of high SST records as well. Although warming is found throughout the Mediterranean basin, the spatial variability found leads to the division of the basin into three distinct subareas regarding warming.

Cyclone Fani: the tug-of-war between regional warming and anthropogenic aerosol effects

Before Cyclone Amphan took place in 2020, Cyclone Fani (May 2019) is the strongest pre-monsoon cyclone in the Bay of Bengal (BOB) since 1991, killing 90 people in eastern India and Bangladesh while causing US$1.81 billion of damages. Fani developed during a period of high concentration of anthropogenic aerosols in the BOB with abnormally high sea surface temperature (SST), thereby presenting an opportunity to understand the compound effects of atmospheric aerosols and regional climate warming on a tropical cyclone. A quantitative attribution analysis was conducted using the Weather Research and Forecasting model with chemistry (WRF-Chem) run at the convection-permitting (4 km) grid spacing, accompanied by an ensemble of coarser-resolution simulations to quantify the uncertainty. The removal of post-1990 trends in the tropospheric variables and SST from WRF-Chem’s initial conditions (IC) and boundary conditions (BC, including the lateral and lower boundary conditions) resulted in a reduction of cyclone precipitation by about 51% during the 5 d of April 28-May 2. The removal of tropospheric warming shows approximately twice as strong an effect on Fani (39% reduction in precipitation) as that of SST warming (22% reduction). When aerosol’s direct and indirect effects were removed from the simulations, i.e., no aerosol influence on radiation and cloud microphysics, Fani initially strengthened but later weakened, as measured by geopotential height and precipitation amounts. These results suggest that aerosol and its interaction with the atmosphere acted to mitigate the strengthening effect of anthropogenic warming on Fani, but was not strong enough to entirely counteract it. Although the ensemble of coarser simulations appears to overestimate Cyclone Fani in terms of precipitation, the direction of the effects is in agreement with that obtained from the 4 km simulations. Given the increasing anthropogenic aerosols in the BOB, future attribution studies using more sophisticated dynamical aerosol models on BOB tropical cyclones are urged.

Marine Heatwaves in the Arctic Region: Variation in Different Ice Covers

AbstractThis study analyzes marine heatwaves (MHWs) in the Arctic for its variation in multiyear ice (MYI), first‐year ice (FYI), and open‐water areas. Results show that there is a significant annual growth in MHW frequency, duration, and intensity in the FYI region, especially for intensity. Since 2005, MHW in FYI increases remarkably in summer and the extent of the affected area continues to grow northward. Particularly, severe MHW events mainly occur in the area where sea ice concentration ranges between 0.1 and 0.5. Stratification in the FYI area impedes the deep mixing and downward transmission of energy from solar radiation, resulting in an anomalously high sea surface temperature in the FYI area. The implication is that MHW will keep growing as the extent of FYI in the Arctic increases.

Symbiodiniaceae diversity of Palythoa tuberculosa in the central and southern Red Sea influenced by environmental factors

Sea surface temperatures (SST) and chlorophyll a concentrations (Chl a) in the southern Red Sea have wide variations based on distance from the coast. To understand how these variations can affect the diversity of symbionts hosted by reef-associated organisms, we conducted a study in the central and southern Red Sea to examine the diversity of Symbiodiniaceae hosted by the zooxanthellate zoantharian Palythoa tuberculosa at different distances from the coast: offshore (FBO), midshelf (FBM) and inshore (FBI) of Farasan Banks, and inshore at Thuwal (TI). Genomic DNA was extracted from 198 specimens, followed by amplification of the ribosomal DNA internal transcribed spacer 2 (ITS-2) and noncoding region of the chloroplast plastid minicircle (psbAncr). Durusdinium and six lineages of Cladocopium (Pt-1-a, Pt-1-b, Pt-1-c, Pt-1-d, Pt-3-a, Pt-3-b) were identified based on sequences of the two marker regions. Changes in composition of Symbiodiniaceae lineages were observed from FBI (high SST, high Chl a) to FBO (low SST, low Chl a). Molecular variance analyses showed that distance from coast was the most likely predictor of differences in Cladocopium lineages. Multinomial logistic regression analysis showed a transition among different Cladocopium lineages as SST increased. One Cladocopium lineage, Pt-1-b, demonstrated higher prevalences at high SSTs and increased in prevalences at the same rate as thermotolerant Durusdinium. Additionally, Cladocopium lineage Pt-3-a had a high affinity to low Chl a concentrations. This study demonstrates that environmental variations in SSTs and Chl a concentrations are significant predictors for the diversity of dominant Symbiodiniaceae within individual host P. tuberculosa colonies. We theorize that flexibility with different lineages of Symbiodiniaceae allows generalist P. tuberculosa to live across a wide range of environments in the southern Red Sea.

Seasonal abundance and diel behavior of roughneck shrimps (species of Rimapenaeus Pérez Farfante & Kensley, 1997) (Decapoda: Dendrobranchiata: Penaeidae) in northwestern Florida Bay, Florida, USA

Abstract A large number of roughneck shrimps, Rimapenaeus Pérez Farfante & Kensley, 1997, were collected in northwestern Florida Bay, southern Florida over four consecutive years (2000–2003) of monthly sampling during new-moon periods. Juveniles of Rimapenaeus spp. were more abundant than pink shrimp Farfantepenaeus duorarum (Burkenroad, 1939) juveniles, which are well-recognized and abundant inhabitants of Florida Bay. High Rimapenaeus spp. abundance was unexpected because the genus was previously reported only as occasional in Florida Bay. The populations of Rimapenaeus spp. were composed of late postlarvae and immature juveniles, suggesting that the northwestern border of Florida Bay serves as a nursery ground for this species. A clear seasonal recruitment pattern was observed with large peaks of postlarvae and small juveniles occurring in summer-fall and large juveniles in spring. The summer-fall peaks occurred during months with high mean water level and sea surface temperature; these two factors significantly predicted Rimapenaeus spp. abundance. Overnight hourly behavioral studies revealed that Rimapenaeus spp. juveniles were almost exclusively present in the water column during the dark hours of the ebb tide during current speed minimum. Juvenile abundance significantly differed between moon phases with shrimps being virtually absent during the illuminated full moon. These results indicate that Rimapenaeus spp. are phototactic negative, which may explain the low presence of this species in previous Florida Bay surveys conducted during daylight hours. This study highlights the previously unrecognized contribution of the abundance of juveniles of Rimapenaeus spp. to benthic-oriented crustacean communities of western Florida Bay and its border at the southwestern Florida Shelf.

Atmospheric Forcing of the High and Low Extremes in the Sea Surface Temperature over the Red Sea and Associated Chlorophyll-a Concentration

Taking advantage of 37-year-long (1982–2018) of high-quality satellite datasets, we examined the role of direct atmospheric forcing on the high and low sea surface temperature (SST) extremes over the Red Sea (RS). Considering the importance of SST in regulating ocean physics and biology, the associated impacts on chlorophyll (Chl-a) concentration were also explored, since a small change in SST can cause a significant impact in the ocean. After describing the climate features, we classified the top 5% of SST values (≥31.5 °C) as extreme high events (EHEs) during the boreal summer period and the lowest SST values (≤22.8 °C) as extreme low events (ELEs) during the boreal winter period. The spatiotemporal analysis showed that the EHEs (ELEs) were observed over the southern (northern) basin, with a significant warming trend of 0.027 (0.021) °C year−1, respectively. The EHEs were observed when there was widespread less than average sea level pressure (SLP) over southern Europe, northeast Africa, and Middle East, including in the RS, leading to the cold wind stress from Europe being relatively less than usual and the intrusion of stronger than usual relatively warm air mass from central Sudan throughout the Tokar Gap. Conversely, EHEs were observed when above average SLP prevailed over southern Europe and the Mediterranean Sea as a result of the Azores high and westward extension of the Siberian anticyclone, which led to above average transfer of cold and dry wind stress from higher latitudes. At the same time, notably less wind stress due to southerlies that transfer warm and humid air masses northward was observed. Furthermore, physical and biological responses related to extreme stress showed distinct ocean patterns associated with each event. It was found that the Chl-a concentration anomalies over the northern basin caused by vertical nutrient transport through deep upwelling processes are the manifestation of the superimposition of ELEs. The situation was the opposite for EHEs due to the stably stratified ocean boundary layer, which is a well-known consequence of global warming.

The effect of wind and temperature to phytoplankton biomass during blooming season in Barents Sea

The Barents Sea is the most productive sea in the Arctic. The main causes of phytoplankton spring blooms are studied for a decadal time period of 2003–2013 at the region of (70 °N-80 °N, 30 °E-40 °E) in Barents Sea. Due to the rapidly ice melt in the southern region (70 °N-75 °N), almost no ice left after year 2005, sea surface temperature (SST) and wind speed (WIND) are two main dominant factors influencing phytoplankton blooming in the southern region. Ice melt is another important factor of phytoplankton blooming in the northern region (75 °N–80 °N). SST and CHL had positive correlations during blooming season but negative correlations during summer time. The lower SST in spring could result in earlier blooming in the region. Higher SST and higher WIND could result in later blooming. Positive NAO after April 2013 caused higher SST in 2013. Increasing WIND would cause CHL reduced accordingly. Blooming period is from late April to late May in the southern region, and 1–2 weeks later in the northern region. During blooming season, SST was less than 4 °C and WIND was less than 10 m/s. The higher winds (over 15 m/s) in early spring would brought more nutrients from bottom to surface and cause higher blooming (near 10 mg/m3 in year 2010) after WIND is reduced to 5−8 m/s. Higher WIND (around 10 m/s) could generate longer blooming period (more than a week) during late May in the southern region. Decrease of WIND and increase of melting ice, with slightly increase of SST and decrease of mixed layer depth (MLD), are all the factors of phytoplankton blooming in late spring and early summer.

Spatial and interannual variability of presettlement tropical fish assemblages explained by remote sensing oceanic conditions

Understanding the interannual effect of various environmental factors on biodiversity distribution is fundamental for developing biological monitoring tools. The interannual variability of environmental factors on presettlement fish assemblages (PFAs) has been so far under investigated, especially in Madagascar. Numerous explanatory variables including local hydro-dynamic conditions recorded during the sampling night, characteristics of the benthic substrate and remotely sensed oceanic conditions (RSOC) were used to explain the spatio-temporal variability of PFAs in southwestern Madagascar. Gradient forest analyses were used to hierarchically classify the effect of these explanatory variables on the PFAs for two sites and during two different recruitment seasons. RSOC variables appeared to better explain the PFAs than the local variable and the characteristics of the benthic substrate. The PFAs caught in water masses with coastal characteristics were better explained than those with open water characteristics. This spatial variability is hypothesised to be linked to differences in feeding conditions among water masses. The gradient forest analyses also highlighted the complexity of predicting PFAs as the species for which abundances were better explained by RSOC variables varied between years. This interannual variability was mainly explained by the interannual variation of chlorophyll a (Chl a) concentration, wind and surface current, with better prediction obtained during the year with high Chl a values associated with high averaged sea surface temperature. These findings suggest the importance of forecasting Chl a concentrations, taking into account the impact of tropical storms and climate variability in order to predict PFAs in the future.

Persistence of high sea surface temperature (> 30°C) in Tomini Bay

Hot Event is a phenomenon with high sea surface temperature > 30°C, which can influence the global climate. Tomini Bay which is categorized as the semi-enclosed waters have the daily appearance of SST >30°C. The purpose of this research is to investigate and determine the mechanism for the occurrence of high and constant SST (>30°C) in Tomini Bay. We found that the phenomenon of constant high SST (> 30°C) in Tomini Bay is influenced by the weak wind speed by less than 4 m/s. The existence of Sulawesi topography and the Togian Islands block the incoming wind and reduce the wind speed. Moreover, the percentage of SST (>30°C) in the middle of Tomini Bay higher than in the western area of Tomini Bay. This might be influenced by the shallow bathymetry in the middle of the Tomini Bay which increases the effectiveness of the heating process in this area.

El Niño Driven Changes in Global Fire 2015/16

El Niño years are characterised by a high sea surface temperature anomaly in the Equatorial Pacific Ocean, which leads to unusually warm and dry conditions over many fire-prone regions globally. This can lead to an increase in burned area and emissions from fire activity, and socio-economic and environmental losses. Previous studies using satellite observations to assess the impacts of the recent 2015/16 El Niño found an increase in burned area in some regions compared to La Niña years. Here, we use the dynamic land surface model JULES to assess how conditions differed as a result of the El Niño by comparing simulations driven by observations from the year 2015/16 with mean climatological drivers of temperature, precipitation, humidity, wind, air pressure and short and long-wave radiation. We use JULES with the interactive fire module INFERNO to assess the effects on precipitation, temperature, burned area, and the associated impacts on the carbon sink globally and for three regions: South America, Africa and Asia. We find that the model projects a variable response in precipitation, with some areas including northern South America, southern Africa and East Asia getting drier, and most areas globally seeing an increase in temperature. As a result, higher burned area is simulated with El Niño conditions in most regions, although there are areas of both increased and decreased burned area over Africa. South America shows the largest fire response with El Niño, with a 13% increase in burned area and emitted carbon, corresponding with the largest decrease in carbon uptake. Within South America, peak fire occurs from August to October across central-southern Brazil, and temperature is shown to be the main driver of the El Niño-induced increase in burned area during this period. Combined, our results indicate that although 2015/16 was not a peak year for global total burned area or fire emissions, the El Niño led to an overall increase of 4% in burned area and 5% in emissions compared to a ‘No El Niño’ scenario for 2015/16, and contributed to a 4% reduction in the terrestrial carbon sink.

Influences of West Pacific Sea Surface Temperature on Covarying Eurasian Droughts Since the Little Ice Age

The Western Pacific Warm Pool (WP), with the highest sea surface temperature (SST) in the world, has strong impacts on the drought variations in Eurasia. However, since the little ice age (1250–1850, LIA), the co-climatic drought pattern due to WP warming in Eurasia remains unclear. This is a long-term warming background for the current warming period (CWP). In this paper, we use both instrumental data and 1625 tree-ring width records from Eurasia to investigate the drought patterns in both modern and historical periods. This study revealed two seesaw precipitation patterns, namely the Central Asia–Mongolia (CAMO) and Northern Europe–Southern Europe (NESE) patterns. When the Western Pacific Warm Pool sea surface temperature (WPSST) is high, precipitation increases in Central Asia and Northern Europe, and decreases in Mongolia and southern Europe. When the positive (negative) phase event of the El Niño–Southern Oscillation (ENSO) occurs, the WPSST is reduced (increased), and the decreases (increases) of precipitation in Central Asia and Northern Europe and the increases (decreases) in precipitation in Mongolia and southern Europe are more obvious. The CAMO dipole has been strengthened since the LIA. The CAMO dipole is positively correlated with solar radiation and Northern Hemisphere temperature, and negatively correlated with Pacific decadal oscillations (PDO).

Contrasting effects of coastal upwelling on growth and recruitment of nearshore Pacific rockfishes (genus Sebastes)

Knowledge of processes underlying recruitment is critical for understanding marine population dynamics and their response to ocean climate. We investigated the relationship between coastal upwelling and early life history of black rockfish (Sebastes melanops), a midwater aggregating species, and CQB rockfishes (a solitary benthic species complex including Sebastes caurinus, Sebastes maliger, and Sebastes auriculatus), between two oceanographically distinct years on the west coast of Vancouver Island, Canada. We analysed otolith microstructure to determine parturition and settlement dates, pelagic durations, and pre- and postsettlement growth rates. High CQB rockfish recruitment in 2005 was associated with prolonged downwelling and warm ocean temperatures, late parturition dates, fast presettlement growth, short pelagic durations, and small size-at-settlement. In contrast, high black rockfish recruitment in 2006 was associated with strong upwelling and cool ocean temperatures, slow presettlement growth, and protracted pelagic durations. Presettlement growth of both rockfish complexes increased with high sea surface temperature, but was unrelated to chlorophyll a concentration. Our results indicate that the same oceanographic conditions give rise to fast presettlement growth and short pelagic durations for both groups, but that different factors lead to strong recruitment in each.

The biogeochemistry and oceanography of the East African Coastal Current

The East African Coastal Current (EACC) is the dominant oceanographic influence along the coastlines of Tanzania and Kenya yet formal descriptions of the biogeochemical characteristics of these waters remain fragmented or poorly defined. Whilst the region remains undersampled, and information for many parameters is limited or even absent, the region is not understudied and complex patterns, due in part to the changing monsoon seasons, can be identified from extant observations. A critical distinction between the neritic waters of the narrow East African continental shelf, which may be more influenced by local tidal currents and terrestrial inputs, and the oligotrophic surface waters of the deeper offshelf region under the influence of the EACC can be drawn, which cautions against the extrapolation of trends or seasonal patterns from limited datasets more widely throughout the region. Permanently N-limited, low NO3−:PO43− surface waters coupled with high (>25 °C) sea surface temperatures are a key feature of the EACC Ecoregion and likely responsible for the presence of a regionally important population of the nitrogen fixing cyanobacterium Trichodesmium, though information on another key requirement, iron, is lacking. Phytoplankton diversity, abundance and the spatiotemporal variability of phytoplankton populations are considered poorly known due to limited sampling efforts. Recent and growing recognition of high coral biodiversity, high reef fish species endemism, of widespread reductions in mangrove forest coverage, and growing anthropogenic pressures on coastal waters suggest that the region deserves greater multidisciplinary study. Efforts to anticipate climate induced changes to these waters, which are expected to impact local fisheries with substantial socioeconomic impacts, would benefit from greater efforts to synthesise existing biogeochemical data, much of which resides within grey literature sources, theses, project reports, remains inaccessible or has been lost. Future biogeochemical and oceanographic observational efforts should simultaneously explore shelf and deeper offshelf waters to determine shelf-to-ocean linkages and the spatiotemporal variability of parameter fields whilst also bridging the gap to research efforts on coral biodiversity, fisheries and marine management activities due to recognised gaps in underlying scientific data to support decision making in these areas.

Weekly sea surface temperature from SNPP-VIIRS data using open source software

The objective of this study is to make weekly mean sea surface temperature (SST) from SNPP-VIIRS satellite data. The data used were SST data every afternoon pass, from 13 to 19 May 2019. The data were obtained from Remote Sensing Technology and Data Center, LAPAN. From 12 samples data used showed that pixel size of each data are different, with range between 0.006737548 - 0.006858158 degree. The pixel size should be exactly the same to do data overlay. Then, the pixel size was resized become 0.00675 degree. This process was carried out using Reprojection Menu in QGIS software. The next process was calculating weekly mean SST every pixel. The mean SST was calculated only on pixels that have SST values. The calculation was not carried out on cloud, cloud shadow, land, and out of coverage data. The tolerance of coordinate position between pixels are less than 0.5 of pixel size. Weekly mean SST calculation process was executed using mean function in R software. The result of mean SST showed some possible error SST values. The errors were found in these conditions: 1) in coastal areas where possible mixed pixels of land and water 2) near cloud, where possible mixed pixel of cloud, cloud shadow, and water, 3) pixels with (extremely) high SST values near clouds. To overcome these conditions, some median type filters were applied. Therefore, weekly mean SST from SNPP-VIIRS data that smooth and minimum cloud cover can be obtained.

The effect of vertical ocean mixing on the tropical Atlantic in a coupled global climate model

Sea surface temperature (SST) biases in the tropical Atlantic are a long-standing problem among coupled global climate models (CGCMs). They occur in equilibrated state, as well as in initialised seasonal to decadal simulations. The bias is typically characterised by too high SST in upwelling regions and associated errors of wind and precipitation. We examine the SST bias in the state-of-the-art CGCM EC-Earth by means of an upper ocean heat budget analysis. Horizontal advection processes affect the SST bias development only to a small extent, and surface heat fluxes mostly dampen the warm bias. Subgrid-scale upper ocean vertical mixing is too low in EC-Earth when compared to estimates from reanalysis data, potentially giving rise to the warm bias. We perform sensitivity experiments to examine the effect of enhanced vertical mixing on the SST bias in quasi equilibrium present day climate and its impact on projected climate change. Enhanced mixing in historical simulation mode ({text {MixUp}}_{pr}) reduces the SST bias in the tropical Atlantic compared to the control experiment ({text {Control}}_{pr}). Associated atmospheric biases of precipitation and surface winds are also reduced in {text {MixUp}}_{pr}. We further perform climate projections under the RCP8.5 emission scenario ({text {Control}}_{fu} and {text {MixUp}}_{fu}). Under increasing greenhouse gas forcing, the tropical Atlantic warms by up to 4.5,^{circ }{text {C}} locally, and maritime precipitation increases in boreal winter and spring. We show that the vertical mixing parameterisation influences future climate. In {text {MixUp}}_{fu}, SSTs remain 0.5,^{circ }{text {C}} colder in boreal winter and spring, but increase with the same amplitude in summer and fall. The strength and location of the projected intertropical convergence zone also depends on the ocean vertical mixing efficiency. The rain band moves southward in summer, and its strength increases in winter in {text {MixUp}}_{fu} as compared to {text {Control}}_{fu}.

Southern hemisphere tropical cyclones: A critical analysis of regional characteristics

AbstractThe destructive nature of tropical cyclones poses a risk to the regions where they occur during and after landfall. Southern hemisphere countries are usually more vulnerable to these risks and impacts due to their lower adaptive capacity. Research for the northern hemisphere has comprehensively explored the nature of tropical cyclones. This information has since been applied to long‐term adaptation plans and short‐term evacuation plans. This study interrogates the characteristics and nature of Southern Hemisphere tropical cyclones and critically explores their differences to Northern Hemisphere storm characteristics. The differences found between the hemispheric storm activities include seasonality, number of storms and the latitudinal position at which these storms undergo genesis and intensification. Similarities were found in storm intensity, which was observed to increase with the time taken to reach maximum lifetime intensity. Higher sea surface temperatures were similarly found to be a major factor associated with increased intensity and lifetime of Southern Hemisphere tropical cyclones. Tropical cyclone seasonality is also centred around the warmer months within each hemisphere. Compared to the Northern Hemisphere the tropical cyclone seasonal length indicates no increase. The magnitude of sea surface temperature increase is also lower in the Northern Hemisphere. These fundamental links observed with temperature in both hemispheres implicates climate warming and its impact on tropical cyclones in both hemispheres, regardless of their seasonality and frequency.

Predicting coral-reef futures from El Ni\xf1o and Pacific Decadal Oscillation events

El Niño Southern Oscillation (ENSO) events modulate oceanographic processes that control temperature and productivity in tropical waters, yet potential interactions with low frequency climate variability, such as the Pacific Decadal Oscillation (PDO), are poorly understood. We show that ENSO and PDO together predicted (i) maximum sea-surface temperatures (SST), which were associated with coral bleaching and declines in coral cover, and (ii) maximum chlorophyll-a concentrations, which were associated with high densities of coral-predatory Acanthaster starfish, across the tropical north Pacific Ocean since 1980. Asynchrony between the positive PDO and negative ENSO (i.e., La Niña) was associated with peaks in annual SST. By contrast, synchrony between the positive PDO and positive ENSO (i.e., El Niño) was associated with peaks in chlorophyll-a. Both conditions led to ecological disturbances and significant loss of coral cover, however, spatial models revealed where impacts to reefs were expected under varying climate scenarios. The 2015/17 ENSO event was coupled with a positive PDO and resulted in high SST and Acanthaster abundances in eastern Micronesia, while positive coral growth occurred in western Micronesia. Our novel approach for forecasting coral growth into the future may be applicable to other oceanic regions with differing oceanographic modulators.

Gillnet fishers’ knowledge reveals seasonality in depth and habitat use of cod (Gadus morhua) in the Western Baltic Sea

AbstractPractical and applied knowledge of local fishers can help to improve our understanding of target species ecology and fisheries management decisions. In the Western Baltic Sea (WBS), the spatio-temporal distribution of cod is still largely unknown despite decades of research. We studied changes in cod distribution by obtaining information on temporal depth and habitat use of cod from commercial gillnet fishers using semi-directed interviews supplemented by at-sea observer data. Linear and non-linear regression analyses revealed significant relationships between depth use of cod and sea surface temperature (SST) as well as thermal stratification. Moreover, habitat use was related to SST and residence depth of cod. Areas deeper than 15 m were favoured from late December until March during low SST and a mixed water column (spawning) and also from July until August during high SST and strong thermal stratification (summer aestivation). Shallower areas were favoured during the rest of the year. The depth and habitat use displayed distinct seasonal up- and downslope movements of cod. This study highlights the importance of shallow-water and structured habitats for cod in the WBS and the value of local knowledge held by fishers for a better understanding of the distributional dynamics of important marine resource populations.

Forced and Unforced Decadal Behavior of the Interhemispheric SST Contrast during the Instrumental Period (1881–2012): Contextualizing the Late 1960s–Early 1970s Shift

AbstractThe sea surface temperature (SST) contrast between the Northern Hemisphere (NH) and Southern Hemisphere (SH) influences the location of the intertropical convergence zone (ITCZ) and the intensity of the monsoon systems. This study examines the contributions of external forcing and unforced internal variability to the interhemispheric SST contrast in HadSST3 and ERSSTv5 observations, and 10 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) from 1881 to 2012. Using multimodel mean fingerprints, a significant influence of anthropogenic, but not natural, forcing is detected in the interhemispheric SST contrast, with the observed response larger than that of the model mean in ERSSTv5. The forced response consists of asymmetric NH–SH SST cooling from the mid-twentieth century to around 1980, followed by opposite NH–SH SST warming. The remaining best-estimate residual or unforced component is marked by NH–SH SST maxima in the 1930s and mid-1960s, and a rapid NH–SH SST decrease around 1970. Examination of decadal shifts in the observed interhemispheric SST contrast highlights the shift around 1970 as the most prominent from 1881 to 2012. Both NH and SH SST variability contributed to the shift, which appears not to be attributable to external forcings. Most models examined fail to capture such large-magnitude shifts in their control simulations, although some models with high interhemispheric SST variability are able to produce them. Large-magnitude shifts produced by the control simulations feature disparate spatial SST patterns, some of which are consistent with changes typically associated with the Atlantic meridional overturning circulation (AMOC).