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Southern Hemisphere tree rings as proxies to reconstruct Southern Ocean upwelling

The Southern Ocean carbon sink is a balance between two opposing forces: CO₂absorption at mid-latitudes and CO₂ outgassing at high latitudes. Radiocarbon analysis can be used to constrain the latter, as upwelling waters outgas old CO₂, diluting atmospheric radiocarbon content. We present tree-ring radiocarbon measurements from Aotearoa / New Zealand and Chile. We show that low radiocarbon in Aotearoa / New Zealand’s Motu Ihupuku / Campbell Island is linked to outgassing in the critical Antarctic Southern Zone.

Quantifying the soil sink of atmospheric hydrogen: a full year of field measurements from grassland and forest soils in the UK

We measured soil hydrogen (H₂) fluxes from two field sites, a managed grassland and a planted deciduous woodland, with flux measurements of H₂ covering full seasonal cycles. We estimate annual H₂ uptake of −3.1 ± 0.1 and −12.0 ± 0.4 kg H₂ ha⁻¹ yr⁻¹ for the grassland and woodland sites, respectively. Soil moisture was found to be the primary driver of H₂ uptake, with the silt/clay content of the soils providing a physical barrier which limited H₂ uptake.

Marine snow morphology drives sinking and attenuation in the ocean interior

Key parameters representing the gravity flux in global models are sinking speed and vertical attenuation of exported material. We calculate, for the first time, these parameters in situ in the ocean for six intermittent blooms followed by export events using high-resolution (3 d) time series of 0–1000 m depth profiles from imaging sensors mounted on an Argo float. We show that sinking speed depends not only on size but also on the morphology of the particles, with density being an important property.

Occupancy history influences extinction risk of fossil marine microplankton groups

We examine how change in a species’ geographic range size over time influences that species’ extinction risk. We analyze instantaneous range size and range size change and how these terms relate to extinction risk in marine microplankton. We find that both the instantaneous range size and the change in range size are informative predictors of extinction. Using predictive models, we also assess extinction probability in four extant groups.

Distribution of alkylamines in surface waters around the Antarctic Peninsula and Weddell Sea

During the PolarChange expedition, volatile alkylamines, important players in nitrogen cycling and cloud formation, were measured in Antarctic waters using a high-sensitivity method. Trimethylamine was the dominant alkylamine in marine particles, associated with nanophytoplankton. Dissolved dimethylamine likely originated from trimethylamine degradation, while diethylamine sources remain unclear. These findings confirm the biological origin of alkylamines in polar marine microbial food webs.

Simulating vertical phytoplankton dynamics in a stratified ocean using a two-layered ecosystem model

Phytoplankton contribute to half of Earth’s primary production, but not a lot is known about subsurface phytoplankton, living at the base of the sunlit ocean. We develop a two-layered box model to simulate phytoplankton seasonal and interannual variations in different depth layers of the ocean. Our model captures seasonal and long-term trends of the two layers, explaining how they respond to a warming ocean, furthering our understanding of how phytoplankton are responding to climate change.

Phylogeochemistry: exploring evolutionary constraints on belemnite rostrum element composition

Belemnite rostrum geochemistry is used as a proxy in palaeoceanography. Evolutionary patterns in element ratios (Mg/Ca, Sr/Ca, Mn/Ca, and Fe/Ca) from belemnite rostra based on a literature dataset are assessed. These proxy data reflect a complex interplay between evolutionary, ontogenetic, environmental, kinetic, and diagenetic effects. We coin the new term “phylogeochemistry” for this interdisciplinary research field.

Sedimentary ancient DNA insights into foraminiferal diversity near the grounding line in the western Ross Sea, Antarctica

Ancient foraminiferal DNA is studied in five Antarctic cores with sediments up to 25 kyr old. We use a standard and a new, more effective marker, which may become the next standard for paleoenvironmental studies. Much less diverse foraminifera occur on slopes of submarine moraines than in open-marine settings. Soft-walled foraminifera, not found in the fossil record, are especially abundant. There is no foraminiferal DNA in tills, suggesting its destruction during glacial redeposition.

Cold-water coral mounds are effective carbon sinks in the western Mediterranean Sea

Cold-water coral mounds are large structures on the seabed that are built by corals over thousands of years. They are regarded as carbonate sinks, with a potentially important role in the marine carbon cycle, but more quantitative studies are needed. Using sediment cores, we calculate the amount of carbon that has been stored in two mounds over the last 400 000 years. We provide the first numbers and show that up to 19 times more carbon is accumulated in mounds than on the common seafloor.

Cenozoic pelagic accumulation rates and biased sampling of the deep-sea record

We provide a new compilation of rates at which sediments deposited in the deep sea over the last 70 million years. We highlight a bias, linked to the drilling process, that makes it more likely for high rates to be recovered for younger sediments than for older ones. Correcting for this bias, the record shows, contrary to prior estimates, a more stable history, thus providing some insights on the past mismatch between physico-chemical model estimates and observations.

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