Alfred Wegener Institute for Polar and Marine Research
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Technical note: Large offsets between different datasets of seawater isotopic composition – an illustration of the need to reinforce intercalibration efforts
Get PDFAbstract. We illustrate offsets in surface seawater isotopic composition between recent public datasets from the Atlantic Ocean and the subtropical southeastern Indian Ocean. The observed offsets between datasets often exceed 0.10 ‰ in δ18O and 0.50 ‰ in δ2H. They might in part originate from different sampling of seasonal, interannual, or spatial variability. However, they likely mostly originate from different instrumentations and protocols used to measure the water samples. Estimation of the systematic offsets is required before merging the different datasets in order to investigate the spatiotemporal variability of isotopic composition in the world ocean surface waters. This highlights the need to actively share seawater isotopic composition samples dedicated to specific intercomparison of data produced in different laboratories and to promote best practices, a task to be addressed by the new Scientific Committee of Oceanic Research (SCOR) working group 171.
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Geographical distribution of two acoustic fin whale (Balaenoptera physalus) populations across the Weddell Sea
Get PDFUnderstanding and identifying population-specific acoustic features is crucial to passive acoustic monitoring-based remote sensing of population distributions. Fin whales are known to produce 20-Hz pulses, often accompanied by a simultaneous higher frequency (HF) component. The centre frequency of this component has been found to differ regionally, presumably representing a population-specific acoustic characteristic. Within the Southern Ocean, five distinct HF components have been identified so far, two of which are present in the Atlantic Sector of the Southern Ocean (ASSO) with peak frequencies around 86 and 99 Hz. This study investigates the extent to which these HF components indicate distinct acoustic fin whale populations and their spatial distribution across the ASSO. By automatically analysing passive acoustic data from 2013, across 10 recording positions, our data show that while the 99-Hz component was detected at seven recording positions throughout the ASSO, the 86-Hz HF component is only present in its western area, centred around the Western Antarctic Peninsula. Additional 2019 data from the Western Antarctic Peninsula confirmed the consistent presence of the 86-Hz component, suggesting that these components are robust indicators of distinct acoustic populations. Knowledge on population-specific key habitats is key to strategic and effective conservation efforts
Distinct Impacts of Increased Atlantic and Pacific Ocean Heat Transport on Arctic Ocean Warming and Sea Ice Decline
Get PDFIncreased ocean heat transport (OHT) to the Arctic Ocean from the Atlantic and Pacific oceans contributes to Arctic Ocean warming and sea ice decline in a warming climate, processes known as Atlantification and Pacification, respectively. However, the separate impacts of these OHTs and their magnitudes remain unclear. This study uses a fully coupled climate model (FIO-ESM v2.1) to investigate the specific impacts of increased Atlantic and Pacific OHTs on Arctic Ocean temperature, sea ice extent, and sea ice concentration. Our sensitivity experiments reveal that increased Atlantic OHT affects the temperature of the entire Arctic Ocean with the greatest impacts found in the Barents Sea and Eurasian Basin and at intermediate depths of the Arctic basin. The warming extent and efficiency from increased Atlantic OHT is considerably greater than that from Pacific OHT. Without warming of the Atlantic Water inflow, the rate of Arctic Ocean warming would decrease by approximately 50%. Increased Pacific OHT mainly affects the upper ocean in the Pacific sector, including the Chukchi Sea, East Siberian Sea, and Canada Basin. Increased OHT from both the Atlantic and Pacific oceans leads to notable sea ice decline with distinct regional and seasonal variations. Increased Atlantic OHT contributes to sea ice decline across most of the Arctic Ocean, particularly in the Barents Sea, the Kara Sea, and the central Arctic. In contrast, increased Pacific OHT leads to sea ice loss dominantly in the Pacific sector, including the Chukchi, the East Siberian, and the Beaufort seas
Too cold, too saturated? Evaluating climate models at the gateway to the Arctic
Get PDFThe Arctic wintertime energy and moisture budgets are largely controlled by the advection of warm,
moist air masses from lower latitudes; the cooling and drying of these air masses inside the Arctic; and the export
of cold, dry air masses. Climate models have substantial difficulties in representing key processes in these air-
mass transformations, including turbulence under stable stratification and mixed-phase cloud processes. Here,
we use radiosonde profiles of temperature and moisture and surface radiation observations from Ny-Ålesund,
Svalbard (1993–2014), to assess the properties of air masses being imported into and exported from the central
Arctic in CMIP6 climate models. In the free troposphere, models tend to be cold-biased, especially for the
coldest temperatures, and relative humidity in most models is closer to saturation with respect to ice than what
is observed. In the analysed models, supersaturation with respect to ice tends to be better represented with
two-moment microphysics. The overall distribution of column-integrated precipitable water in models matches
well with observations. Cold and dry biases are stronger in air masses being exported from the Arctic than
those entering the Arctic. This suggests that the previously reported cold bias in the Arctic in CMIP6 models is
probably due to errors in local thermodynamic processes
From global to national GHG budgets: the REgional Carbon Cycle Assessment and Processes-3 (RECCAP3)
Get PDFGlobal Carbon Budget 2024
Get PDFAbstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize datasets and methodologies to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC) are based on land-use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly, and its growth rate (GATM) is computed from the annual changes in concentration. The global net uptake of CO2 by the ocean (SOCEAN, called the ocean sink) is estimated with global ocean biogeochemistry models and observation-based fCO2 products (fCO2 is the fugacity of CO2). The global net uptake of CO2 by the land (SLAND, called the land sink) is estimated with dynamic global vegetation models. Additional lines of evidence on land and ocean sinks are provided by atmospheric inversions, atmospheric oxygen measurements, and Earth system models. The sum of all sources and sinks results in the carbon budget imbalance (BIM), a measure of imperfect data and incomplete understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the year 2023, EFOS increased by 1.3 % relative to 2022, with fossil emissions at 10.1 ± 0.5 GtC yr−1 (10.3 ± 0.5 GtC yr−1 when the cement carbonation sink is not included), and ELUC was 1.0 ± 0.7 GtC yr−1, for a total anthropogenic CO2 emission (including the cement carbonation sink) of 11.1 ± 0.9 GtC yr−1 (40.6 ± 3.2 GtCO2 yr−1). Also, for 2023, GATM was 5.9 ± 0.2 GtC yr−1 (2.79 ± 0.1 ppm yr−1; ppm denotes parts per million), SOCEAN was 2.9 ± 0.4 GtC yr−1, and SLAND was 2.3 ± 1.0 GtC yr−1, with a near-zero BIM (−0.02 GtC yr−1). The global atmospheric CO2 concentration averaged over 2023 reached 419.31 ± 0.1 ppm. Preliminary data for 2024 suggest an increase in EFOS relative to 2023 of +0.8 % (−0.2 % to 1.7 %) globally and an atmospheric CO2 concentration increase by 2.87 ppm, reaching 422.45 ppm, 52 % above the pre-industrial level (around 278 ppm in 1750). Overall, the mean of and trend in the components of the global carbon budget are consistently estimated over the period 1959–2023, with a near-zero overall budget imbalance, although discrepancies of up to around 1 GtC yr−1 persist for the representation of annual to semi-decadal variability in CO2 fluxes. Comparison of estimates from multiple approaches and observations shows the following: (1) a persistent large uncertainty in the estimate of land-use change emissions, (2) low agreement between the different methods on the magnitude of the land CO2 flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the mean ocean sink. This living-data update documents changes in methods and datasets applied to this most recent global carbon budget as well as evolving community understanding of the global carbon cycle. The data presented in this work are available at https://doi.org/10.18160/GCP-2024 (Friedlingstein et al., 2024).
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The Expeditions PS145/1 and PS145/2 of the Research Vessel POLARSTERN to the Atlantic Ocean in 2024
Get PDFImpact of snow thermal conductivity schemes on pan-Arctic permafrost dynamics in the Community Land Model version 5.0
Get PDFThe precise magnitude and timing of permafrost-thaw-related emissions and their subsequent impact on the global climate system remain highly uncertain. This uncertainty stems from the complex quantification of the rate and extent of permafrost thaw, which is influenced by factors such as snow cover and other surface properties. Acting as a thermal insulator, snow cover directly influences surface energy fluxes and can significantly impact the permafrost thermal regime. However, current Earth system models often inadequately represent the nuanced effects of snow cover in permafrost regions, leading to inaccuracies in simulating soil temperatures and permafrost dynamics. Notably, the Community Land Model (CLM5.0) tends to overestimate snowpack thermal conductivity over permafrost regions, resulting in an underestimation of the snow insulating capacity. Using a snow thermal conductivity scheme better adapted for the snowpack typically found in permafrost regions, we seek to resolve thermal insulation underestimation and assess the influence of snow on simulated soil temperatures and permafrost dynamics. Evaluation using two Arctic-wide soil temperature observation datasets reveals that the new snow thermal conductivity scheme reduces the cold-soil temperature bias (root-mean-square error, RMSE Combining double low line 3.17 to 2.4 °C, using remote sensing data; RMSE Combining double low line 3.9 to 2.19 °C, using in situ data), demonstrates robustness through sensitivity analysis under lower tundra snow densities, and addresses the overestimation of permafrost extent in the default CLM5.0. This improvement highlights the importance of incorporating realistic snow processes in land surface models for enhanced predictions of permafrost dynamics and their response to climate change