Warm Years Research Articles

Evidence of 2024 Summer as the Warmest During the Last Four Decades in the Aegean, Ionian, and Cretan Seas

The summer of 2024 witnessed record-high sea surface temperatures (SST) across the Aegean, Ionian, and Cretan Seas (AICS), following unprecedented air heatwaves over the sea under a long-term warming trend of 0.46 °C/decade for the mean atmospheric temperature (1982–2024). The respective mean SST trend for the same period is even steeper, increasing by 0.59 °C/decade. With mean summer surface waters surpassing 28 °C, particularly in the Ionian Sea, the southern Cretan, and northern Aegean basins, this summer marked the warmest ocean conditions over the past four decades. Despite a relatively lower number of marine heatwaves (MHWs) compared to previous warm years, the duration and cumulative intensity of these events in 2024 were the highest on record, reaching nearly twice the levels seen in 2018, which was the warmest until now. Intense MHWs were recorded, especially in the northern Aegean, with extensive biological consequences to ecosystems like the Thermaikos Gulf, a recognized MHW hotspot. The strong downward atmospheric heat fluxes in the summer of 2024, following an interannual increasing four-decade trend, contributed to the extreme warming of the water masses together with other met-ocean conditions such as lateral exchanges and vertical processes. The high temperatures were not limited to the surface but extended to depths of 50 m in some regions, indicating a deep and widespread warming of the upper ocean. Mechanisms typically mitigating SST rises, such as the Black Sea water (BSW) inflow and coastal upwelling over the eastern Aegean Sea, were weaker in 2024. Cooler water influx from the BSW decreased, as indicated by satellite-derived chlorophyll-a concentrations, while upwelled waters from depths of 40 to 80 m at certain areas showed elevated temperatures, likely limiting their cooling effects on the surface. Prolonged warming of ocean waters in a semi-enclosed basin such as the Mediterranean and its marginal sea sub-basins can have substantial physical, biological, and socioeconomic impacts on the AICS. This research highlights the urgent need for targeted monitoring and mitigation strategies to address the growing impact of MHWs in the region.

Assessing temporal variability in durum wheat performance and stability through multi-trait mean performance selection in Mediterranean climate

Durum wheat, a staple crop in Italy, faces substantial challenges due to increasing droughts and rising temperatures. This study examines the grain yield, agronomic traits, and quality of 41 durum wheat varieties over ten growing seasons in Southern Italy, utilizing a randomized complete block design. Notably, most varieties were not repeated between trials and 45% of the data was missing. The results indicate that the interaction between genotype and environment (GEI) significantly impacted all traits. High temperatures, elevated vapor pressure deficit (VPD), and water deficits severely affected yield and quality during warm years, while cooler years with favorable water availability promoted better growth and higher yields. Broad-sense heritability (H²) was generally low, suggesting that environmental factors played a major role in the observed traits. However, some traits, such as grain yield, ears per square meter, plant height, bleached wheat, thousand-grain weight, and hectoliter weight exhibited moderate to high heritability of the mean genotype (h²mg), indicating their potential for effective selection in breeding programs. Correlation analyses revealed strong connections between certain traits, such as protein content, and gluten index as well as between grain yield, and spike per square meter. Using the Multi-Trait Mean Performance Selection (MTMPS) index, the study identified six top-performing varieties. Among these, Antalis (G4) and Core (G18) consistently demonstrated strong adaptability and stability across different environments, particularly in hotter, drier conditions. Furio Camillo (G31) also exhibited valuable traits. This study highlights the challenges and complexities of breeding durum wheat for improved yield and quality in the face of climate change.

Tree-ring maximum latewood density reveals unprecedented warming and long-term summer temperature in the upper Indus Basin, northern Pakistan

Understanding long-term temperature variability in the Upper Indus Basin (UIB), northern Pakistan, and its driving mechanisms is challenging due to the scarcity of long observational records and available literature. In this study, we reconstructed a 651-year (1370–2020 CE) warm-season (March–September) temperature record using the tree-ring maximum latewood density (MXD) of blue pine (Pinus wallichiana). The reconstruction explains 57 % of the variance in actual temperature during the common calibration period (1972–2020 CE). Our analysis identified ten high-temperature periods (temperature > 20.9 °C) and nineteen low-temperature periods (temperature < 19.8 °C), with the coldest years being 1392, 1707, 1817, and 1837, and the warmest years being 2013, 2016, 2017, and 2018. Spatial correlation analysis reveals a significant positive correlation with field temperature, predominantly in neighboring regions, and a significant negative correlation with relative humidity and precipitation. Multi-taper spectral analysis shows inter-annual (1.9, 2.5, 2.7, 5.5 years) and interdecadal (11, 18, 23, 25, 40, 71 years) cycles, suggesting a potential linkage with the Atlantic Multidecadal Oscillation (AMO). The negative linkage between our reconstruction and the region's standardized Palmer Drought Severity Index (scPDSI) indicates that continued temperature increase could result in severe drought in northern Pakistan in the near future. During the 20th century, the UIB experienced two distinct warming phases: 1948–1970 CE and 1994–2020 CE. The warming rate during 1994–2020 CE was 0.5 °C higher, indicating unprecedented recent warming. The reconstructed temperature record also demonstrates a large-scale spatiotemporal signal and a strong connection with most recorded volcanic eruptions. These findings enhance our understanding of long-term temperature variability in the region, highlighting the significance of MXD in reconstructing past temperature patterns.

Perturbations in a pelagic food web during the NE Pacific Large Marine Heatwave and persistent harmful diatom blooms

Unprecedented warm ocean conditions, driven by the Large Marine Heatwave (LMH) and the 2015-16 El Niño in the Northeast Pacific favored pervasive toxigenic Pseudo-nitzschia spp. blooms that caused widespread ecological impacts, but little is known about the magnitude to which marine food webs were altered. Here, we assessed the trophic transfer of domoic acid (DA; a neurotoxin) and changes in trophic position from multiple key species during the peak of the LMH and El Niño in 2015 in comparison with 2018, a reference non-anomalous warm year. DA and amino acid nitrogen isotopes (δ15N AAs) were quantified using liquid and gas chromatography mass spectrometry, respectively. Our integrative approach revealed extremely high levels of DA in anchovy viscera (> 3000 μg/g) with contrasting baseline values (δ15N Phe) for southern California fish. These results together with data from northern CA revealed an unforeseen latitudinal isotopic variation in key DA vectors along California, possibly driven by anomalous restructuring of water masses. At the regional level, the observed cross-shore differences in baseline isotope values and DA toxicity suggest distinct pathways for DA trophic transfer for nearshore vs. offshore sites. Given the high levels of environmental disturbance during the LMH and persistence of toxigenic P. australis blooms, our resultant higher trophic position proxies in 2015 compared to 2018 were particularly unexpected. Such results highlight complex trophic interactions, where the trophic status of some species increased while others decreased in response to changes in net primary productivity, and biodiversity, and abundance of forage species. Our study demonstrates the use of δ15N AAs to identify pathways of N and DA trophic transfer and to quantify shifts in animal trophic position, a critical facet of understanding the response of food webs to climate change and DA production.

Temporal increase in ticks and pathogen prevalence in the small mammal part of the Lyme disease cycle in northern Europe

AbstractLyme disease is an emerging infectious disease and the most common vector‐borne zoonosis in the northern hemisphere. The pathogen that causes Lyme disease in Europe is vectored by the generalist tick Ixodes ricinus, and the emergence of Lyme disease is partly linked to how climate warming affects tick distribution and abundance. However, we lack long‐term data on tick infestations and infection prevalence in the main hosts involved in the transmission cycle. Here, we quantified the temporal trends (2014–2022) of I. ricinus infestations and the prevalence of Borrelia burgdorferi sensu lato in small mammalian hosts and linked annual variation to host abundance and climate in Norway. We found that tick infestations for both larvae (21% per year [95% CI 18–25]) and nymphs (18% [11–26]), and infection prevalence (14% [8–20]) increased over the period and were negatively associated with rodent abundance. Additionally, warmer years were associated with increased larval tick infestations on hosts. The combination of a temporal increase in both larval tick infestation and infection prevalence in hosts likely results in increased production of infected nymphs. Thus, we provide one mechanistic step toward understanding the Lyme disease emergence at northern latitudes of Europe.

Vertical bedrock shifts reveal summer water storage in Greenland ice sheet

The Greenland ice sheet (GrIS) is at present the largest single contributor to global-mass-induced sea-level rise, primarily because of Arctic amplification on an increasingly warmer Earth1–5. However, the processes of englacial water accumulation, storage and ultimate release remain poorly constrained. Here we show that a noticeable amount of the summertime meltwater mass is temporally buffered along the entire GrIS periphery, peaking in July and gradually reducing thereafter. Our results arise from quantifying the spatiotemporal behaviour of the total mass of water leaving the GrIS by analysing bedrock elastic deformation measured by Global Navigation Satellite System (GNSS) stations. The buffered meltwater causes a subsidence of the bedrock close to GNSS stations of at most approximately 5 mm during the melt season. Regionally, the duration of meltwater storage ranges from 4.5 weeks in the southeast to 9 weeks elsewhere. We also show that the meltwater runoff modelled from regional climate models may contain systematic errors, requiring further scaling of up to about 20% for the warmest years. These results reveal a high potential for GNSS data to constrain poorly known hydrological processes in Greenland, forming the basis for improved projections of future GrIS melt behaviour and the associated sea-level rise6.

Global and regional climate in 2023

Abstract2023 was the warmest year on record with a global mean temperature of 1.45 ± 0.12 degC above pre‐industrial levels, surpassing the previous record (from 2016) by 0.17 degC. The onset of El Niño in early July was accompanied by record‐breaking land and sea‐surface temperatures, with June to September all exceeding previous monthly temperature records, and July and August being the hottest months on record. Sea‐surface temperatures have attained record highs for all months since March 2023 and Antarctic sea ice reached record lows throughout the year.

Long-term climate-based sizing and economic assessment of air-water heat pumps for residential heating

This study presents a novel methodology for sizing air–water heat pumps (ASHP) for space heating and hot water supply in buildings. Utilizing long-term local climatic data, the developed tool determines the coefficient of performance (COP) and feasibility of ASHP. The sizing algorithm incorporates peak heat demand, unitary final energy demand, and seasonal heat demand across various detached house sizes. Annual local heating system operation time and key economic indicators are derived for each case across 3 European countries. A new approach is precise investigation of 10-year outdoor temperatures and apply it to heat pump (HP) modeling, which enabled a distinction between so-called warm and cold years. The results underscore substantial variations in net present value (NPV) between warm and cold years, illustrating the critical influence of precise climate data on the performance of HPs. The study revealed that for a 160 m2 house in Poland, annual electricity consumption by HPs ranged from 3736 kWh during warm years to 12,908 kWh during cold years, showing a significant variation in performance based on climate conditions. The comprehensive tool allows for precise adjustments of heating systems to actual local climate conditions, improving both economic and environmental outcomes. This comparative assessment aids in the optimal selection of HPs, ensuring energy efficiency and sustainability in residential heating systems. Building on studies from various climatic regions, this work addresses the knowledge gap in performance and explores the feasibility of HP in a changing climate using precise modeling techniques.

Renovating Post-First-Energy-Regulation Housing: Achieving Nearly Zero-Energy buildings under typical and extreme warm conditions in a temperate European city

Decarbonising the built environment is essential for achieving the 2050 European objectives. Multi-family buildings comprise nearly half of Europe’s building stock, yet there is no regulation mandating all housing renovations to be Nearly Zero-Energy Buildings (NZEBs). This paper highlights the role of NZEB renovation for residential buildings constructed between the first energy regulations, after the first oil crisis, and the EPBD 2002 implementation (post-first-energy-regulation housing), as a pivotal factor towards energy transition. In Spain, this period (1980–2006) encompasses approximately 45% of existing dwellings. A case study was conducted in a city with a Cfb temperate climate, focusing on the most representative residential typology of the target period: the linear block. The study evaluates its current state and defines potential measures to meet NZEB requirements, achieving zero consumption when renovation of thermal envelope is combined with heat recovery systems, heat pumps, and PV panels.This research is based on energy simulations for two climate scenarios: the typical meteorological year (TMY, official series 1970–2000) and the most extreme warm year (EWY, 2022) in Spain. Results indicate active cooling systems are necessary for NZEB renovations in Spanish Cfb climates. Furthermore, low-temperature radiators significantly reduce heating consumption, while splits are the most suitable cooling systems. This study shows Spain is not adequately preparing its housing stock to face climate change, as most typical renovation works are based on official weather files that need updating to reflect harsher summer conditions. Finally, the study aims to encourage new policies and enhance existing regulations to address rising temperatures and heatwaves.

Reappraising Cladophialophora bantiana phaeohyphomycosis in France: retrospective nation-based study

Cladophialophora bantiana is one of the most virulent phaeohyphomycetes, typically causes non-angiogenic single (or sometimes multiple) cystic brain lesions, and has resulted in a mortality rate of up to 70%.Most Cbantiana cases are described either in a series of isolated reports or in very small cohorts. The aim of this retrospective nation-based study was to share the data on Cbantiana phaeohyphomycosis cases reported in France and French overseas territories over the past two decades to improve understanding of this disease. Patients with Cbantiana infection were processed through the active surveillance programme of invasive fungal infections launched by the National Reference Center for Mycoses and Antifungals, Institut Pasteur (Paris, France), and the French Surveillance Network of Invasive Fungal Infections, which involved 29hospitals from mainland France and overseas French territories. Onlyproven and probable cases of infection, according to the revised and updated consensus definitions from the European Organization for Research and Treatment of Cancer and Mycoses Study Group, were included in the study. Patients were diagnosed or confirmed, or both, using a polyphasic approach at the Institut Pasteur between 2002and2022. Patients were separated into two groups: those with CNS involvement and those with no CNS involvement. Theprimary outcome was the survival rate. A total of 23patients with a Cbantiana invasive infection were included during the study period (Jan 1, 2002, to Dec 31, 2022). The median age was 56years in the CNS involvement group and 65years in the non-CNS involvement group. Until 2021, the annual number of cases varied between zero and two, with six cases observed in 2022, the warmest year recorded in France since 1900. CNS involvement was observed in 15 (65%) patients, including three disseminated cases; skin and soft tissue involvement in seven (30%) patients and an isolated lung infection in one case. Diabetes was observed in five patients, and any immunodepression factor was observed in 14 (61%) of 23patients. When considering only patients with CNS involvement, 9-month survival appeared higher in patients who underwent exeresis or large drainage (three [75%] of four patients vs three [27%] of 11patients; p=0·24) and significantly higher in those treated for 2or more weeks with triple antifungal therapy (liposomal amphotericin Bplus posaconazole and flucytosine; seven [78%] of nine patients vs one [17%] of six patients; p=0·040). Two patients were treated with excision surgery alone (one patient with success, and the other patient lost to follow-up). This study shows that the clinical presentations and underlying medical conditions of Cbantiana infections are more diverse than previously described. It also emphasises a significant difference in mortality rate between those with and without CNS involvement. The prognosis improved when surgery was performed and triple antifungal therapy was administered. Such rare and devastating invasive fungal infections should be managed by a multidisciplinary team. Santé Publique France.

Variability and Composition of Mysid Assemblages in a Northwest Iberian Estuary: Insights from a 10-Year Data Series

Long-term temporal studies have been used to assess the effects of climate change on mysid populations and their complex ecological interplay within heterogeneous ecosystems. This study is the first to investigate the mysid community in the Mondego estuary, western Portugal, for a decade, from 2003 to 2012. Monthly data collected from five stations along the estuary was used to investigate variations in mysid assemblage composition, patterns, phenology, and the interactions with environmental variables. Thirteen taxa were found in the assemblages. The community was dominated by Mesopodopsis slabberi, which was found in great numbers in the upper estuarine region. Praunus flexuosus and Schistomysis spiritus dominated the assemblages in the middle estuary, while Gastrossacus spinifer and Heteromysis formosa were very abundant at the mouth of the estuary. Overall, mysids were mostly present during autumn periods, when local environmental factors such as water temperature and chlorophyll-a concentrations influenced assemblage abundances. The high productivity of the system played a pivotal role in fostering greater species abundance. However, lower abundances were detected during warmer years, further evidencing changes in these key species’ communities under future climatic scenarios of increasing water temperatures.

Influence of Mini Warm Pool Extent on Phytoplankton Productivity and Export in the Arabian Sea

The Arabian Sea is a highly productive tropical ecosystem of the Indian Ocean that supports high fluxes of particulate organic carbon to the mesopelagic zone from two distinct periods of elevated biological productivity associated with the semiannual reversals of the monsoonal wind system. There are now strong indications that the Arabian Sea’s monsoonal wind patterns and hydrographic conditions are being impacted by long-term temperature increases, but the consequences of these changes on primary production and carbon export to the mesopelagic zone are unknown. This is especially true for the summer monsoon period when cloud cover obscures much of the Arabian Sea basin and therefore precludes remotely sensed ocean color measurements for estimating phytoplankton biomass and productivity. Here we overcome this limitation by using a database of bio-optical profiles from Biogeochemical Argo floats collected over the last decade to evaluate the impact of interannual temperature increases on Arabian Sea primary production and carbon export. We classify individual years of float observations based on the spatial extent of the Arabian Sea Mini Warm Pool that appears in the southeast Arabian Sea before the onset of the summer monsoon. This mini warm pool, which begins to build in winter and collapses with the onset of the summer monsoon in late spring, has gained considerable interest on account of its influence on the timing of the onset of the summer monsoon. We observed a 35 percent decrease in primary production during the summer monsoon phytoplankton bloom in strong warm pool years, and a 13 percent decrease in particle stocks in the upper mesopelagic zone following the peak of the bloom. Decreases in production and export were additionally accompanied by a decrease in average particle size, indicating a shift from larger cells like diatoms that appear from fertilization of the oligotrophic waters to smaller phytoplankton size classes in response to a deepening of the thermocline and increased stratification of the water column. These results suggest changes in phytoplankton community structure and further decreases in primary production and carbon export in the Arabian Sea in response to future warming.

Study of the feature of the temperature regime of the Mykolaiv and region in the context of the issue of climate change

Climate change is one of the most important and acute environmental problems of our time. It includes a complex of changes, such as rising ambient temperatures, changes in precipitation patterns, rising sea levels, and more frequent extreme weather events. According to the Intergovernmental Panel on Climate Change (IPCC), the average global temperature has risen by about 1.1°C since the late nineteenth century. Projections point to a possible increase of 1.5°C by the middle of this century unless significant measures are taken to reduce greenhouse gas emissions. On the basis of the above, the paper analyzes trends in changes in atmospheric air temperature on the territory of risky agriculture in the South of Ukraine in the Mykolaiv region.The purpose of the study: to determine and substantiate the regularities of changes in the temperature regime of Mykolaiv and Mykolaiv region in the context of climate change.Research results. The values of temperature characteristics for the year and season in Mykolaiv and Mykolaiv region during 1991−2023 are analyzed. In Mykolaiv, about 60-67 days with a negative average daily air temperature and about 32 days with a negative maximum daily air temperature are recorded. The duration of the period with a negative minimum air temperature can be an average of 93 days per year: 64 in winter, 16 in spring and 14 in autumn. At the same time, on a large territory of the Mykolaiv region, autumn is warmer than spring. The average seasonal air temperature is 10.6°C, the average maximum temperature is 15.4°C, and the average minimum temperature is 6.4°C. In the Northern Black Sea region, both maximum and minimum temperatures in autumn are higher than in spring. The dynamics of changes in average annual temperatures in the city of Mykolaiv in the period from 1980 to 2023 are analyzed. A stable linear trend towards a gradual increase in average annual temperatures has been determined. The warmest year for this observation period is 2023, the coldest are 1985 and 1987. It is determined that the rate of increase in average temperature is 0.61°C for every ten years. Maximum temperatures are increasing at a rate of 0.0884°C per year and minimum temperatures are decreasing at a rate of 0.0136°C per year. Every year, the average annual temperature increases by approximately 0.021°С. The largest number of days accompanied by heat stress (up to 90%) is observed in July – August. Thus, changes in air temperature indicate a significant change in the temperature regime of the entire climate system of the region, and the consequences of climate change may be predominantly negative and will intensify in the future.

Warming events and their causes at the Bering Sea section B in summer of 1999–2019

Based on hydrological data for the Bering Sea from 1999 to 2019 during the Chinese National Arctic Research Expeditions (CHINAREs), along with oceanographic and meteorological data from the National Centers for Environmental Information (NCEI) and the European Centre for Medium-Range Weather Forecasts (ECMWF), we investigated trends in summer at the Bering Sea section B over the past 20 years and their underlying causes. The results revealed a pronounced rise in temperature at the Bering Sea section B in 2003, 2014, 2016, 2018, and 2019, suggesting a shift towards a new phase of warmth starting in 2014. In warm years (2003, 2014, 2016, 2018, and 2019), the mean maximum temperature in the upper layer in the basin north of 57°N and on the continental shelf were roughly 2.7 °C, 2.6 °C higher than that in cold years (1999, 2008, 2010, and 2012). Additionally, the mean minimum temperature of the cold water in the middle layer in the basin was roughly 0.7 °C higher in the warm years compared to the cold years. This difference between the warm and cold years was evident in the heat content: the average heat content in the upper to middle layers in the basin north of 57°N and on the continental shelf were about 1.2 and 0.9 GJ/m2 higher, respectively, in the warm years than the cold years. However, there was a modest warming trend in the basin south of 57°N, and the temperature in the mid-layer on the continental shelf showed year-to-year stability, in contrast to the significant warming observed elsewhere. Further study suggested that temperature fluctuation in the basin was closely tied to seasonal 2-m air temperature. In addition, the southern basin, divided at 57°N, experienced larger positive or negative anomalous wind stress curl compared to the northern basin. This discrepancy resulted in differing causes of temperature variation between the two regions. Temperature change in the upper layer on the continental shelf was attributed to an increase in cumulative net heat flux resulting from reduced sea ice, while the temperature in the middle layer on the continental shelf was limited by the enhanced density gradient between the upper and middle layer caused by melt ice, preventing significant warming. Overall, the thermal state for the Bering Sea section B was influenced by a combination of factors, including net heat flux, sea ice, and atmospheric conditions, contributing to the year-to-year variation characterized by alternating cold and warm regimes.

Spatial and temporal variability of temperature, precipitation, and solar radiation in Magdalena department, Colombia from 2000 to 2022

Climate variability analysis is crucial for understanding current patterns and predicting future climate behavior. This knowledge is essential for decision-making about mitigation and reduction activities to combat climate change from those activities that may cause abrupt changes in climate dynamics. The present study analyzed climate variability in the Magdalena department, Colombia, over a 22-year period. Temperature, solar radiation, and precipitation data from NASA's Giovanni reanalysis and simulation are used with data from local meteorological stations. Statistical homogeneity and trend tests were applied to find climate patterns using RStudio software. The results showed that the years 2010 and 2011 were the wettest in the time series. Conversely, 2015 was the warmest year on record in the time series. This analysis provides a more comprehensive understanding of the climate variability in the region, laying the foundation for future studies on this subject.

Interannual Variability in Seed Germination Response to Heat Shock in Cistus ladanifer

Mediterranean climates, characterised by hot and dry summers, have predictable fire regimes, and many species with physical seed dormancy (PY) thrive after wildfires. While it is well known that PY is released after heat shock in these species, intraspecific variation in seed response to heat is less understood. This research explores, for the first time, the variability in the traits of Cistus ladanifer seeds from the same central Spain population over eight years. It examines seed germination and viability under different heat shocks and the relationships among seed traits and climatic variables. While the response to heat shock remained constant over the years studied, achieving the highest germination percentages after heat shock at 100 °C, seed germination varied between years, and environmental conditions affected seed traits. Seed moisture content was negatively correlated with the maximum summer temperatures, and seed viability was positively related to annual precipitation. Germination at 100 °C was lower in warmer years as more seeds did not break their PY. In conclusion, despite the fact that PY appears to be genetically determined, it also depends on the environmental conditions experienced by the mother plant. This interannual phenotypic variability may help Cistus ladanifer to cope with the increasingly unpredictable conditions imposed by climate change.

Vertical distribution of mesopelagic fishes deepens during marine heatwave in the California Current

Abstract Marine heatwaves can impact the distribution and abundance of epipelagic organisms, but their effect on deep pelagic communities is unclear. Using fisheries acoustics data collected in the Central California current from 2013 to 2018, we found that during the warmest years of a large marine heatwave (2015–2016), the estimated center of mass depth of mesopelagic fishes deepened by up to 100 m compared to preheatwave conditions. Using a generalized additive model, we evaluated which biophysical factors may have driven these changes and found that light, dynamic height anomaly, and acoustic backscatter explained 81% of the variability in depth. We attribute the vertical shift by mesopelagic fishes into deeper waters to heatwave-driven compression of upwelling habitat that indirectly increased the amount of light reaching mesopelagic depths. Our results suggest that mesopelagic fishes are interconnected with, and thus sensitive to changes in near-surface oceanographic conditions, which could lead to cascading effects on vertical carbon export and the availability of mesopelagic fishes as prey for top predators under future climate conditions.

Biennial variability of boreal spring surface air temperature over India

In this study, we report significant biennial variability or oscillation (BO) in the boreal spring (March–May) Surface Air Temperature (SAT) over India and unravelled the causative mechanisms. The positive phase of the BO exhibit significant seasonal warming over India, whereas seasonal cooling is observed during the negative phase of BO. Heat wave days are more during the positive phase of BO compared to negative or neutral phase. The positive (negative) phase of BO is generally coherent with the central (eastern) Pacific warming (cooling) years. The anomalous low-level divergence associated with low-level anticyclonic circulation induces less cloudiness and intense surface solar radiation ovr India during the positive phase, favouring surface warming. The evolution of some positive and/or negative phases of BO without any large scale forcing from the equatorial Pacific suggested the possibility of alternate pathways. The strong anomalous upper-level (at 200 hPa) anticyclonic circulation provoked by mid-latitude Rossby waves is found contributing to the positive phase, thereby highlighting the role of dominant mid-latitude pathways in the biennial SAT variability in addition to El Niño forcing. The sinking motion associated with persistent high, and the associated adiabatic compression also supported surface heating during the positive phase of BO. On the other hand, the mid-latitude Rossby wave induced upper-level cyclonic circulation is found contributing to the negative phase. The sinking motion associated with persistent high, and the associated adiabatic compression also supported surface heating during the positive phase of BO. In contrast, negative soil temperature anomalies and high latent heat flux release to the atmosphere supported surface cooling during the negative phase.

More sensitive microbial responses to the interactive effects of warming and altered precipitation in subsoil than topsoil of an alpine grassland ecosystem.

Subsoil is a large organic carbon reservoir, storing more than half of the total soil organic carbon (SOC) globally. Conventionally, subsoil is assumed to not be susceptible to climate change, but recent studies document that climate change could significantly alter subsoil carbon cycling. However, little is known about subsoil microbial responses to the interactive effects of climate warming and altered precipitation. Here, we investigated carbon cycling and associated microbial responses in both subsoil (30-40 cm) and topsoil (0-10 cm) in a Tibetan alpine grassland over 4 years of warming and altered precipitation. Compared to the unchanged topsoil carbon (β = .55, p = .587), subsoil carbon exhibited a stronger response to the interactive effect of warming and altered precipitation (β = 2.04, p = .021), that is, warming decreased subsoil carbon content by 28.20% under decreased precipitation while warming increased subsoil carbon content by 18.02% under increased precipitation.Furthermore, 512 metagenome-assembled genomes (MAGs) were recovered, including representatives of phyla with poor genomic representation. Compared to only one changed topsoil MAG, 16 subsoil MAGs were significantly affected by altered precipitation, and 5 subsoil MAGs were significantly affected by the interactive effect of warming and precipitation. More than twice as many populations whose MAG abundances correlated significantly with the variations of carbon content, components and fluxes were observed in the subsoil than topsoil, suggesting their potential contribution in mediating subsoil carbon cycling. Collectively, our findings highlight the more sensitive responses of specific microbial lineages to the interactive effects of warming and altered precipitation in the subsoil than topsoil, and provide key information for predicting subsoil carbon cycling under future climate change scenarios.

Approximation of ice phenology of Maine lakes using Aqua MODIS surface temperature data

AbstractStudies of lake ice phenology have historically relied on limited in situ data. Relatively few observations exist for ice out and fewer still for ice in, both of which are necessary to determine the temporal extent of ice cover. Satellite data provide an opportunity to better document patterns of ice phenology across landscapes and relate them to the climatological drivers behind changing ice phenology. We developed a model, the Cumulative Sum Method (CSM), that uses daytime and nighttime surface temperature observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on board the Earth‐observing Aqua satellite to approximate ice in (the onset of ice cover) and ice out from training datasets of 13 and 58 Maine lakes, respectively, during the 2002/2003 through 2017/2018 ice seasons. Ice in was signaled by reaching a threshold of cumulative negative degrees following the first day of the season below 0°C. Ice out was signaled by reaching a threshold of cumulative positive degrees following the first day of the year above 0°C. The comparison of observed and remotely sensed ice‐in dates showed relative agreement with a correlation coefficient of 0.71 and a mean absolute error (MAE) of 9.8 days. Ice‐out approximations had a correlation coefficient of 0.67 and an MAE of 8.8 days. Lakes smaller in surface area and nearer the Atlantic coast had the greatest error in approximation. Application of the CSM to 20 additional lakes in Maine produced a comparable ice‐out MAE of 8.9 days. Ice‐out model performance was weaker for the warmest years; there was a larger MAE of 12.0 days when the model was applied to the years 2019–2023 for the original 58 lakes. The development of this model, which utilizes daily satellite data, demonstrates the promise of remote sensing for quantifying ice phenology over short, temporal scales, and wider geographic regions than can be observed in situ, and allows exploration of the influence of surface temperature patterns on the process and timing of ice in and ice out.