Temperature Records Research Articles

Lipid-biomarker-based sea surface temperature record offshore Tasmania over the last 23 million years

Abstract. The Neogene (23.04–2.58 Ma) is characterised by progressive buildup of ice volume and climate cooling in the Antarctic and the Northern Hemisphere. Heat and moisture delivery to Antarctica is, to a large extent, regulated by the strength of meridional temperature gradients. However, the evolution of the Southern Ocean frontal systems remains scarcely studied in the Neogene. Here, we present the first long-term continuous sea surface temperature (SST) record of the subtropical front area in the Southern Ocean at Ocean Drilling Program (ODP) Site 1168 off western Tasmania. This site is, at present, located near the subtropical front (STF), as it was during the Neogene, despite a 10∘ northward tectonic drift of Tasmania. We analysed glycerol dialkyl glycerol tetraethers (GDGTs – on 433 samples) and alkenones (on 163 samples) and reconstructed the paleotemperature evolution using TEX86 and U37k′ as two independent quantitative proxies. Both proxies indicate that Site 1168 experienced a temperate ∼ 25 ∘C during the early Miocene (23–17 Ma), reaching ∼ 29 ∘C during the mid-Miocene climatic optimum. The stepwise ∼ 10 ∘C cooling (20–10 ∘C) in the mid-to-late Miocene (12.5–5.0 Ma) is larger than that observed in records from lower and higher latitudes. From the Pliocene to modern (5.3–0 Ma), STF SST first plateaus at ∼ 15 ∘C (3 Ma), then decreases to ∼ 6 ∘C (1.3 Ma), and eventually increases to the modern levels around ∼ 16 ∘C (0 Ma), with a higher variability of 5∘ compared to the Miocene. Our results imply that the latitudinal temperature gradient between the Pacific Equator and the STF during late Miocene cooling increased from 4 to 14 ∘C. Meanwhile, the SST gradient between the STF and the Antarctic margin decreased due to amplified STF cooling compared to the Antarctic margin. This implies a narrowing SST gradient in the Neogene, with contraction of warm SSTs and northward expansion of subpolar conditions.

Quantifying Daytime Heating Biases in Marine Air Temperature Observations from Ships

Abstract Marine air temperatures recorded on ships during the daytime are known to be biased warm on average due to energy storage by the superstructure of the vessels. This makes unadjusted daytime observations unsuitable for many applications including for the monitoring of long-term temperature change over the oceans. In this paper a physics-based approach is used to estimate this heating bias in ship observations from ICOADS. Under this approach, empirically determined coefficients represent the energy transfer terms of a heat budget model that quantifies the heating bias and is applied as a function of cloud cover and the relative wind speed over individual ships. The coefficients for each ship are derived from the anomalous diurnal heating relative to nighttime air temperature. Model coefficients, cloud cover, and relative wind speed are then used to estimate the heating bias ship by ship and generate nighttime-equivalent time series. A variety of methodological approaches were tested. Application of this method enables the inclusion of some daytime observations in climate records based on marine air temperatures, allowing an earlier start date and giving an increase in spatial coverage compared to existing records that exclude daytime observations. Significance Statement Currently, the longest available record of air temperature over the oceans starts in 1880. We present an approach that enables observations of air temperatures over the oceans to be used in the creation of long-term climate records that are presently excluded. We do this by estimating the biases inherent in daytime temperature reports from ships, and adjust for these biases by implementing a numerical heat-budget model. The adjustment can be applied to the variety of ship types present in observational archives. The resulting adjusted temperatures can be used to create a more spatially complete record over the oceans, that extends further back in time, potentially into the late eighteenth century.

Characteristics of Marine Heatwaves in the Philippines

Marine Heatwaves (MHWs) are prolonged, discrete, and anomalously warm events, which have recently gained global attention due to their far-reaching effects and reported impacts. Although intensive studies have been carried out at global and regional scales, these events remained understudied in the Philippines – a country with high marine biodiversity. The Philippines is highly vulnerable to the impacts of these extreme events as it lies in the western boundary of the Pacific that is considered as a hotspot for MHWs. The present study used multi-year climatic sea surface temperature (SST) record to detect MHWs in the Philippines. The detected events were then characterized using the standardized metrics. Linear trend analysis was conducted to determine the magnitude and direction of the change of the MHW metrics over time. Decadal trend revealed that MHWs in the Philippines significantly increased from seven MHWs in the 1980s to 37 MHWs in the last decade. Moreover, increased duration was remarkable in 2020 with 276 MHW days. MHW frequency and duration were increasing at a rate almost twice as its neighboring waters. Intensities did not significantly increase with time, but the highest SST anomaly is associated with El Niño Southern Oscillation. Furthermore, the eastern and western region of the Philippines is vulnerable to MHWs, but hotspots are mostly confined in the West Philippine Sea and western tropical Pacific. An in-depth investigation of the drivers of MHWs is recommended to understand the physical mechanisms of the development of these extreme thermal events in the Philippine seas. The findings have significant implications for coastal marine resource management, highlighting the need for adaptive management strategies and increased monitoring and research efforts to mitigate the impacts of MHWs on marine ecosystems and local economies in the Philippines.

Steady decline in mean annual air temperatures in the first 30 k.y. after the Cretaceous-Paleogene boundary

Abstract The Cretaceous-Paleogene (K-Pg) boundary marks one of the five major mass extinctions of the Phanerozoic. The ways in which the climate system responded to a bolide impact and extensive volcanism at this time over different time scales are highly debated. We used the distribution of branched tetraether lipids (brGDGT) from fossil peats at two sites in Saskatchewan, Canada (paleolatitude ~55°N), to generate a high-resolution (millennial) record of mean annual air temperature (MAAT) spanning the last ~4 k.y. of the Cretaceous and the first ~30 k.y. of the Paleogene. Our study shows that MAATs ranged from 16 to 29 °C, with the highest value in the first millennia of the Paleogene. The earliest Paleogene averaged ~25 °C—maintaining or enhancing warmth from the latest Cretaceous—followed by a general cooling to ~20 °C over the following ~30 k.y. No abrupt postboundary cooling (e.g., an “impact winter”) or abrupt warming is evident in our data, implying that if such phenomena occurred, their duration was relatively short-lived (i.e., sub-millennial-scale). Further, no long-term impactor volcanism-driven warming is evident. The range of temperature change observed is considerably greater than that derived from marine proxy records over the same time interval. Our findings therefore more properly place bounds on the magnitude and duration of temperature change on land during this critical interval—the main setting for the demise of nonavian dinosaurs and the rise of mammals.

Thermal conduction in karst terrains dominating cave atmosphere temperatures: Quantification of thermal diffusivity

The relatively stable temperature of most cave interiors is caused by the transfer of the surface atmosphere temperature signal to the karst underground by thermal conduction. Transferring underground thermal signals by conduction implies the amplitude attenuation of the external thermal anomaly as well as a signal delay. The magnitude of these attenuation and delay effects is proportional to the thickness of bedrock cover above the cave and is controlled by the bedrock thermal diffusivity. Here we present 5-year temperature record of Los Pilones Cave, in central Spain, where advection has a limited control on thermal anomalies all year round. Thus, thermal conduction dominates the thermal variability in the cave, with simulations of a 1-D thermal conduction model explaining up to 94% of the variability observed. Thermal attenuation and signal delays are highly correlated with the thickness of bedrock cover (r2 = 0.95 in both cases), enabling the calculation of a thermal diffusivity of 5.07*10−7 ±1.27*10−7 m2/s. The calculated thermal diffusivity is in the range of available values measured in laboratory for carbonate lithologies, although differs beyond uncertainty from the limited number of studies that calculated this value from field observations in karst. Thus, local rock properties significantly impact thermal diffusivities, and more experimental studies are required to show a complete distribution of this value in karst settings. The reported uncertainty, that was calculated using different time windows within the studied period, represents a variability of 23% on the thermal diffusivity. Karst terrains are mostly composed of three phases, rock, air and water, that have different thermal properties. Thus, variability of the water content in the rock porosity through time is likely a significant control on the measured uncertainty. Since temperature in the studied cave has a minor component affected by advection, this cave represents a paradigmatic location to observe the important role of thermal conduction in caves. Therefore, conclusions from this study can be useful to better understand thermal regimes and interannual trends of most cave interiors despite occurrence of variable impacts of seasonal ventilation dynamics in cave temperature records. In addition, the mechanism of thermal conduction results in a thermal decoupling between the surface and cave atmospheres affecting cave microclimate, which has important implications for multiple disciplines interested in karst underground environments.

Mid‐Tropospheric Layer Temperature Record Derived From Satellite Microwave Sounder Observations With Backward Merging Approach

AbstractWe present a new version (v5.0) of the NOAA Center for Satellite Applications and Research (STAR) mid‐tropospheric temperature (TMT) time series. This data set uses a backward‐merging approach to intercalibrate 16 satellite‐based microwave sounding records. The instrument observations included those from the Microwave Sounding Unit (MSU) during 1979–2004, Advanced Microwave Sounding Unit‐A (AMSU‐A) during 1998–2017, and Advanced Technology Microwave Sounder (ATMS) from 2011 to present. A TMT time series during 2002–present based on satellite microwave observations in stable sun‐synchronous orbits was used as a reference in the backward merging process in which earlier satellites were adjusted and merged to the reference. Observations from earlier satellites were recalibrated to remove their calibration drifting errors relative to the reference using sequential overlapping observations. This included removal of spurious warming drifts in the MSU observations onboard NOAA‐11, NOAA‐12, and NOAA‐14 and a spurious cooling drift in the NOAA‐15 AMSU‐A observations. Temperature changes resulting from diurnal sampling drifts were corrected using an observation‐based semi‐physical model developed in this study. Other adjustments included channel frequency differences between MSU and AMSU‐A companion channels and instrument blackbody warm target effect on observed radiances. These adjustments resulted in inter‐consistent TMT records spanning MSU, AMSU‐A, and ATMS. The merged time series produced a global mean TMT trend of 0.092 ± 0.043 K/decade during 1979–2021 and a total tropospheric trend of 0.142 ± 0.045 K/decade after removal of a stratospheric cooling effect in TMT. Remarkably, the total tropospheric trends during the latest half period were nearly doubled the earlier half period over the global ocean.

A 1000‐Year Record of Temperature From Isotopic Analysis of the Deep Critical Zone in Central China

AbstractTemperature proxies for paleoclimate reconstruction have been made typically via ice cores, tree rings, stalagmites, and lake sediments. While extremely useful, these proxies can be limited spatially. Here we sampled a 98 m “soil core” from Loess Plateau of China and examined the relationship between pore water isotopic values and hydroclimate history. We extracted soil pore water for δ18O, δ2H, and 3H and measured chloride concentration. The 3H‐peak at 6 m and chloride mass balance were used to turn depth into calendar year. A 1000 year span was revealed. δ18O and δ2H values between 14–50 m were anomalously low—bracketing well the Little Ice Age period from 1420 to 1870. The identification was consistent with other standard proxies in the region and showed the same temporal dynamics of temperature anomalies. Our study shows the potential of stable isotopes of soil water for paleoclimate reconstruction in deep soils.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Commercial krill fishing within a foraging supergroup of fin whales in the Southern Ocean.

Fast response of vegetation in East Asia to abrupt climatic events during the last deglaciation.

Climate changes had major impacts on the vegetation of East Asia during the last deglaciation. However, the rate and pattern of vegetation succession in response to large-scale climatic events during this interval are controversial. Here, we present well-dated decadal-resolution pollen records from annually laminated Maar Lake Xiaolongwan during the last deglaciation. The vegetation changes were rapid and near-synchronous with millennial-scale climatic events, including Greenland Stadial 2.1a (GS-2.1a), Greenland Interstadial 1 (GI-1), Greenland Stadial 1 (GS-1), and the early Holocene (EH). The vegetation responded in different ways to the different rates of climate change. Vegetation change was gradual [∼1 thousand years (kyr) response time] during the transition between GS-2.1a and GI-1, but it was faster (∼0.4 kyr response time) during the transitions between GI-1, GS-1, and the EH, resulting in different patterns of vegetation succession. Additionally, the amplitude and pattern of vegetation changes resembled those in the records of regional climate change based on long-chain n-alkanes δ13C and stalagmite δ18O, as well as in the mid-latitude Northern Hemisphere temperature record and the Greenland ice core δ18O record. Therefore, the rate and pattern of vegetation succession in the Changbai Mountain of Northeast Asia during the last deglaciation were sensitive to the characteristics of changes in the regional hydrothermal conditions and mid-latitude Northern Hemisphere temperature, which were linked to both high- and low-latitude atmospheric-oceanic dynamics. Overall, our findings reveal a close relationship between ecosystem succession and hydrothermal changes during these millennial-scale climatic events in East Asia during the last deglaciation.

A brGDGT‐Based Reconstruction of Terrestrial Temperature From the Maritime Continent Spanning the Last Glacial Maximum

AbstractThe tropics exert enormous influence on global climate. Despite the importance of tropical regions, the terrestrial temperature history in the Indo‐Pacific Warm Pool (IPWP) region during the last deglaciation is poorly constrained. Although numerous sea surface temperature (SST) reconstructions provide estimates of SST warming from the Last Glacial Maximum to the Holocene, the timing of the onset of deglacial warming varies between records and inhibits determining the forcings driving deglacial warming in the IPWP. We present a 60,000‐year long temperature reconstruction based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) in a sediment core from Lake Towuti, located in Sulawesi, Indonesia. BrGDGTs are bacterial membrane‐spanning lipids that, globally, become more methylated with decreasing temperature and more cyclized with decreasing pH. Although changes in temperature are the dominant control on brGDGTs in regional and global calibrations, we find that the cyclization of the brGDGTs is a major mode of variation at Lake Towuti that records important changes in the lacustrine biogeochemical environment. We separate the influence of lake chemistry changes from temperature changes on the brGDGT records, and develop a temperature record spanning the last 60,000 years. The timing of the deglacial warming in our record occurs after the onset of the deglacial increase in CO2 concentrations, which suggests rising greenhouse gas concentrations and the associated radiative forcing may have forced deglacial warming in the IPWP. Peaks in temperature around 55 and 34 ka indicate that Northern Hemisphere summer insolation may also influence land surface temperature in the IPWP region.

The unprecedented Pacific Northwest heatwave of June 2021

In late June 2021 a heatwave of unprecedented magnitude impacted the Pacific Northwest region of Canada and the United States. Many locations broke all-time maximum temperature records by more than 5 °C, and the Canadian national temperature record was broken by 4.6 °C, with a new record temperature of 49.6 °C. Here, we provide a comprehensive summary of this event and its impacts. Upstream diabatic heating played a key role in the magnitude of this anomaly. Weather forecasts provided advanced notice of the event, while sub-seasonal forecasts showed an increased likelihood of a heat extreme with lead times of 10-20 days. The impacts of this event were catastrophic, including hundreds of attributable deaths across the Pacific Northwest, mass-mortalities of marine life, reduced crop and fruit yields, river flooding from rapid snow and glacier melt, and a substantial increase in wildfires—the latter contributing to landslides in the months following. These impacts provide examples we can learn from and a vivid depiction of how climate change can be so devastating.

Clumped and oxygen isotope sclerochronology methods tested in the bivalve Lucina pensylvanica

Geochemical signatures preserved within the geologic record can be used to reconstruct past mean temperature and seasonality, but in order to accurately apply any geochemical proxy method in the past, a rigorous study of how the recorded proxy is related to temperature in the modern setting must be conducted. Here, we assess the ability of multiple isotope techniques to correctly record mean annual temperature and seasonality in the bivalve Lucina pensylvanica. We compare subannual-resolution δ18O-based, seasonally-targeted and continuous high-resolution (H.R.) clumped isotope (Δ47)-based thermometry methods, as well as multiple data treatment methods for each, to determine which approach best matches known modern temperatures (maximum and minimum absolute temperature and annual temperature range), with the goal of defining the ideal sampling scheme for use on fossil shells. In L. pensylvanica shells collected from 7 sites, we observe neither mean temperature nor seasonal biases. Mean annual temperature is best matched by averaging all seasonally-targeted Δ47-temperatures. Seasonality is best matched by averaging δ18Ocarb-based temperatures from all summers and all winters before taking the difference. Of two data treatment approaches applied to the continuous high-resolution Δ47-based temperatures, “data optimization” is apparently better at resolving smaller seasonal temperature differences. In contrast, “data smoothing” produces a temperature record unbiased by prior assignment of seasonal extremes and has the simultaneous ability to detect subannual variability in δ18Ow. However, accurate application of H.R. Δ47 methods must balance sampling resolution and growth rate. If sampling resolution is high enough relative to the growth rate (∼1 pt./month or better), we recommend continuous high-resolution Δ47-thermometry with data smoothing. If this resolution cannot be achieved due to slow growth rates or insufficient shell size, we recommend pairing subannual δ18Ocarb-based and seasonally-targeted Δ47-based temperature reconstruction to acquire seasonal range in temperature and absolute temperature extremes.

CO2-forced Late Miocene cooling and ecosystem reorganizations in East Asia

In parallel with pronounced cooling in the oceans, vast areas of the continents experienced enhanced aridification and restructuring of vegetation and animal communities during the Late Miocene. Debate continues over whether pCO2-induced global cooling was the primary driver of this climate and ecosystem upheaval on land. Here we present an 8 to 5 Ma land surface temperatures (LST) record from East Asia derived from paleosol carbonate clumped isotopes and integrated with climate model simulations. The LST cooled by ~7 °C between 7.5 and 5.7 Ma, followed by rapid warming across the Miocene-Pliocene transition (5.5 to 5 Ma). These changes occurred synchronously with variations in alkenone and Mg/Ca-based sea surface temperatures and with hydroclimate and ecosystem shifts in East Asia, highlighting a global climate forcing mechanism. Our modeling experiments additionally demonstrate that pCO2-forced cooling would have altered moisture transfer and pathways and driven extensive aridification in East Asia. We, thus, conclude that the East Asian hydroclimate and ecosystem shift was primarily controlled by pCO2-forced global cooling between 8 and 5 Ma.

Reassessing long-standing meteorological records: an example using the national hottest day in Ireland

Abstract. This analysis highlights the potential value in reanalysing early national meteorological records from around the world. These were oftentimes measured via techniques that preceded standardisation of instrumentation and methods of observation and thus could be subject to considerable biases and uncertainties. This analysis uses the techniques pioneered by WMO record assessment teams. The highest currently recognised air temperature (33.3 ∘C) ever recorded in the Republic of Ireland was logged at Kilkenny Castle in 1887. The original observational record however no longer exists. Given that Ireland is now the only country in Europe to have a national heat record that was set in the 19th century, a reassessment of the verity of this record is both timely and valuable. The present analysis undertakes a fundamental reassessment of the plausibility of the 1887 temperature record using methods similar to those used to assess various weather extremes under WMO auspices over recent years. Specifically, we undertake an inter-station reassessment using sparse available records and make recourse to the new and improved 20CRv3 sparse-input reanalysis product. Neither surrounding available stations nor the reanalysis offer substantive support for the Kilkenny record of 33.3 ∘C being correct. Moreover, recent data rescue efforts have uncovered several earlier extreme values, one of which exceeds the Kilkenny value (33.5 ∘C on 16 July 1876 recorded at the Phoenix Park). However, the sparsity of early observational networks, a distinct lack of synoptic support from 20CRv3 for many of the extreme heat values, and the fact that these measurements were obtained using non-standard exposures lead us to conclude that there is grossly insufficient evidence to support any of these 19th century extremes as robust national heat record candidates. Data from the early 20th century onwards benefit from a denser network of stations undertaking measurements in a more standardised manner, many under the direct auspices of Met Éireann and its predecessors, adhering to WMO guidance and protocols. This enables more robust cross-checking of records. We argue that the Met Éireann-recognised 20th century heat record from Boora in 1976 is verified as the most plausible robust national temperature record based upon the synoptic situation and comparisons with nearby neighbouring stations. This measurement of 32.5 ∘C thus likely constitutes the highest reliably recorded temperature measurement in the Republic of Ireland. Ultimately, the formal decision on any reassessment and reassignment of the national record rests with the national meteorological service, Met Éireann.

Can Global Mean Temperatures be Held to 1.5∘C or Less without Major Efforts in Carbon Removal/Geoengineering?

The 2015 international Paris Agreement called for pursuing efforts to limit the changes in climate to 1.5∘C above pre-industrial levels. This study uses two approaches to re-examine this feasibility more fully. The observed trends in the temperature record provide one means to estimate when 1.5∘C will be reached. Examination of the remaining allowed carbon emissions provides another approach. The temperature record and the observed trends in temperature over recent decades suggest that 1.5∘C will be reached by 2032–2042. Consideration of the equivalent amount of CO2 reveals the ranges of 266, 366 and 531 GtCO2-eq still allowed for 67%, 50% and 33% probabilities, respectively, of staying within the temperature limit. At the current rate of emissions, the 50% limit would be reached in eight years. If an emissions reduction of 4% per year beginning in January 2023 is considered, the 67% likelihood for staying within the 1.5∘C limit is passed in 2030 and the 50% likelihood is passed in 2035. As a result, humanity is very unlikely to meet the identified targets needed to keep the global temperature change to 1.5∘C and the SSP1-1.9 scenario assumptions for future emissions toward enabling a limit of 1.5∘C are also extremely unlikely.

Maintenance of the last step of the cold chain: on-farm refrigerator storage and performance

Maintenance of the cold chain post-manufacturing for livestock vaccines is the most important way to ensure maximum product efficacy and safety. Often, it is unknown if refrigerators used for farm storage are operating in the recommended temperature interval (RTI) for vaccine storage of 36°F to 46°F (2°C to 8°C), and whether or not they are able to maintain those temperatures as the ambient room temperature changes. In order to evaluate the performance of different styles of refrigerators on dairy farms and veterinary clinics in the southeast United States, a convenience sample of 20 refrigerators was selected for the placement of digital data loggers to monitor the internal refrigerator and ambient temperatures over 5 months from July to November 2021. The percentage of time that refrigerators spent outside the RTI ranged from 0% to 80% with a median of 22%. The percentage of time outside the RTI was significantly greater for household refrigerators (37%) compared to commercial refrigerators (2.2%), while mini-refrigerators (27%) were intermediate. The estimated mean daily temperature range (MDTR) of household refrigerators (9.5°F, 5.3°C) was also significantly greater than that for commercial (5.4°F, 3°C) or mini (5.8°F, 3.2°C) refrigerators. Implications of the study show the necessity for proper temperature monitoring, staff training and record keeping to ensure vaccine efficacy and product safety, and ultimately improve animal health and productivity.

Strength and variability of the Oligocene Southern Ocean surface temperature gradient

Large Oligocene Antarctic ice sheets co-existed with warm proximal waters offshore Wilkes Land. Here we provide a broader Southern Ocean perspective to such warmth by reconstructing the strength and variability of the Oligocene Australian-Antarctic latitudinal sea surface temperature gradient. Our Oligocene TEX86-based sea surface temperature record from offshore southern Australia shows temperate (20–29 °C) conditions throughout, despite northward tectonic drift. A persistent sea surface temperature gradient (~5–10 °C) exists between Australia and Antarctica, which increases during glacial intervals. The sea surface temperature gradient increases from ~26 Ma, due to Antarctic-proximal cooling. Meanwhile, benthic foraminiferal oxygen isotope decline indicates ice loss/deep-sea warming. These contrasting patterns are difficult to explain by greenhouse gas forcing alone. Timing of the sea surface temperature cooling coincides with deepening of Drake Passage and matches results of ocean model experiments that demonstrate that Drake Passage opening cools Antarctic proximal waters. We conclude that Drake Passage deepening cooled Antarctic coasts which enhanced thermal isolation of Antarctica.

Variability of thermocline temperature in the Bay of Bengal and its response to solar insolation and Indian monsoon over the last 15 kyr

Surface seawater stratification shows a sensitive response to solar insolation and large-scale ocean current, further playing an important role in the air-sea interactions at different time scales. However, the variation of surface seawater structure and its driving mechanism in the tropical Indian Ocean is poorly understood. We present a new record of thermocline temperature (TWT) obtained using oxygen isotope and Mg/Ca-temperature of the planktonic foraminifer Pulleniatina obliquiloculata (P. obliquiloculata) from core BoB-24 in the central Bay of Bengal (BoB). The results indicate that TWT rose rapidly from the Younger Dryas (YD) and persisted at a peak temperature value of 22.5 °C between 10 and 7 cal ka BP, and subsequently reduced by 1.5 °C in the middle Holocene period. The temporal variability of TWT occurred following the boreal summer insolation, associated with tropical climate changes such as the movement of the Inter-tropical Convergence Zone (ITCZ) as well as relevant changes of seasonal Indian monsoons. During the YD period, the southward movement of ITCZ and strengthened Indian winter monsoon (IWM) influenced the deepening of pycnocline, which caused subsurface warming and decreased stratification. During the middle Holocene, the northward return of ITCZ and strengthening of Indian summer monsoon (ISM) led to a stronger surface water stratification and present cooling trend of optimum TWT (10–7 cal ka BP). Furthermore, the millennial TWT changes presented in this study revealed a close link with North Atlantic climate changes, indicating a dynamic action of Atlantic meridional overturning circulation (AMOC).

Bio-loggers inserted in intravaginal sponges, or subcutaneously, as tools to measure body temperature

The body temperature of animals can be measured by thermistors, thermocouples, or radiotelemetry devices that are implanted surgically under the skin, although the suitability of subcutaneous temperature as an indicator of core temperature can be limited because of abnormal temperature readings, probably affected by ambient temperature and animal inactivity. This study compared the use of bio-loggers designed to monitor subcutaneous temperature (Tsub), with their use embedded in intravaginal sponges to measure vaginal temperature (Tvag). Three ewes were implanted with a subcutaneous temperature bio-logger that was configured to record Tsub every 30 min for a month. Ewes were given an intravaginal sponge for 12 days two days later. Inside the sponges were installed programmed bio-loggers that measured Tvag every 5 min. The ambient temperature (Tamb) and relative humidity were monitored using mini data-loggers. Mean Tsub was lower (P < 0.001) during the day (38.02 ± 0.02 °C) than at night (38.10 ± 0.02 °C), with maximum Tsub (38.57 °C) at 20:00 h and minimum temperature (37.36 °C) at 08:00 h; however, mean Tvag was higher (P < 0.001) during the day (38.71 ± 0.01 °C) than at night (38.62 ± 0.01 °C), with maximum Tsub (39.02 °C) at 20:55 h and minimum temperature (38.33 °C) occurred at 08:25 h. Mean Tsub (38.08 ± 0.02 °C) was lower (P < 0.0001) than was Tvag (38.65 ± 0.10 °C) in the daytime and at night (P < 0.001). Both temperatures had a 24-h rhythm (P < 0.0001), but differed (P < 0.001) in the mean midline estimating statistic of rhythm (MESOR) (Tvag: 38.67 ± 0.02 °C, Tsub: 38.09 ± 0.02 °C), amplitude (Tvag: 0.21° ± 0.01C; Tsub: 0.25 ± 0.01 °C), and acrophase (Tvag: 18:27 ± 0.38 h, Tsub: 20:48 ± 0.44 h). The coefficient of correlation between the two temperatures, measured simultaneously for 12 d was 0.644 (P < 0.01), and between Tamb and the two physiological temperatures, measured at the same time throughout the 12 d experiment, was 0.319 (P < 0.01) for Tsub and 0.287 (P < 0.01) for Tvag. The linear regression analysis of the 24 h circadian rhythm in Tsub and Tvag indicated a high coefficient of determination with Tvag (0.9255) and a lower coefficient of determination with Tsub (0.4292). In conclusion, the integration of a mini body temperature logger into a vaginal sponge, or their subcutaneous insertion, provided a continuous and accurate record of body temperature. Furthermore, the strong correlation between mean 24 h circadian Tvag and Tamb, demonstrated the usefulness of Tvag in biometeorological studies in sheep. As an alternative to employing these devices subcutaneously, they can also can be utilized as a biomarker of core body temperature inserted in vaginal sponges.

Coupling of the ecosystems in North China with the East Asian summer monsoon rainfall during the Holocene

The influence of Holocene East Asian Summer Monsoon (EASM) rainfall on ecosystems over northern China remains controversial: delay or synchronization. Here we present Holocene quantitatively reconstructed temperature and salinity records based on alkenone proxies in the Dali Lake from northern China. Our data indicate that the Dali Lake was significantly diluted to a freshwater lake (0.8 ± 0.4 g/L) during ∼11.4–3.8 cal ka BP, relative to the modern brackish state. From the early Holocene (before 8.0 cal ka BP) to the middle Holocene (8.0–5.0 cal ka BP), the average salinity value of Dali Lake decreased by ∼0.3 g/L (ca. 30%), but our reconstructed temperature record shows an increase of ∼2.1 °C. In the context of climate warming, the evaporation was enhanced, and thus the decline in salinity is attributed to the increased precipitation, indicating a mid-Holocene EASM rainfall maximum. After comparing our reconstruction with vegetation data, we proposed that the stable and abundant EASM rainfall promoted the forest expansion and vegetation recovery over northern China during the mid-Holocene, suggesting the coupling of ecosystems and EASM rainfall in North China.