Mechanisms of atmospheric CO₂ growth by 20 ppm from 6000 BCE to the pre-industrial period are still uncertain. We apply the Earth system model MPI-ESM-LR for two transient simulations of the climate–carbon cycle. An additional process, e.g. carbonate accumulation on shelves, is required for consistency with ice-core CO₂ data. Our simulations support the hypothesis that the ocean was a source of CO₂ until the late Holocene when anthropogenic CO₂ sources started to affect atmospheric CO₂.

This study examines how limited water availability during droughts affects water-use efficiency. This metric describes how much carbon an ecosystem can assimilate for each unit of water lost by transpiration. We test how well different water-use efficiency models can capture the dynamics of transpiration decrease due to increased soil-water limitation. Accounting for the interacting effects of radiation and water limitation is necessary to accurately predict transpiration during these periods.

Organic carbon (C) stocks within seasonal wetlands are vulnerable to increased severity and duration of droughts in response to climate change. Here we examined the mechanistic controls on C cycling in seasonally flooded mineral wetland soils. We found that different mechanisms preserve C in surface layers (oxygen limitations) compared to subsurface layers (mineral protection and lack of root C inputs).

The N isotopic composition of nitrate (nitrate δ15N) is a useful tracer of ocean N cycling and many other ocean processes. Here, we use a global compilation of marine nitrate δ15N as an input, training, and validating dataset for an artificial neural network (a.k.a., machine learning) and examine basin-scale trends in marine nitrate δ15N from the surface to the seafloor.

Giant clams including the species Tridacna maxima are unique among bivalves as they live in symbiosis with unicellular algae and generally function as net photoautotrophs. Light is therefore crucial for these species to thrive. We show that net calcification and photosynthetic rates of T. maxima are light dependent, with maximum rates at conditions comparable to 4 m water depth, reflected also in the depth-related distribution in the Red Sea with maximum abundances in shallow sunlit coral reefs.

Boreal peatlands represent an important store of carbon and wildfire can have a significant impact on carbon exchange. We assessed the impact of fire on methane (CH₄) emissions using both a field and laboratory study. We found that fire switched the typical understanding of peatland CH₄ emissions, burned sites having significantly reduced emissions (likely due to reduction in organic matter for CH₄ production) and no relationship with water table, unlike at the unburned site.

This study takes advantage of the GLODAPv2 database to investigate the processes driving the surface ocean dissolved inorganic carbon distribution, with the focus on its latitudinal gradient between the polar oceans and the low-latitude oceans. Based on our quantitative study, we find that temperature-driven CO₂ gas exchange and high-latitude upwelling of DIC- and TA-rich deep waters are the two major drivers, with the importance of the latter not having been previously realized.

Unexpectedly, in sediment traps deployed in the Antarctic Amundsen Sea to catch small sinking particles in the water, large benthic invertebrates such as long and slender worms, baby sea urchins, and small scallops were found. We suggest three hypotheses: lifting of these animals by anchor ice formation and subsequent transport by ice rafting, spending their juvenile period in a habitat underneath the sea ice and subsequent falling, or their active use of the current as a means of dispersal.

In this article, we present the variability and characteristics of dissolved organic matter at the fluvial–marine transition in the Laptev Sea from a unique dataset collected during 11 Arctic expeditions. We develop a new relationship between dissolved organic carbon (DOC) and coloured dissolved organic matter absorption, which is used to estimate surface water DOC concentration from space. We believe that our findings help current efforts to monitor ongoing changes in the Arctic carbon cycle.

The Indian Ocean subtropical gyre is a large oligotrophic area that is likely to adjust to continued warming by increasing stratification, reduced nutrient supply and decreasing biological production. In this study, we investigated concentrations of nutrients and stable isotopes of nitrate. We determine the lateral influence of water masses entering the gyre from the northern Indian Ocean and from the Southern Ocean and quantify the input of nitrogen by N₂ fixation into the surface layer.

We found that peatlands in coastal Sarawak, Borneo, export extremely humified organic matter, which dominates the riverine organic matter pool and conservatively mixes with seawater, while the freshly produced fraction is low and stable in concentration at all salinities. We estimated that terrigenous fractions, which showed high photolability, still account for 20 % of the coastal dissolved organic carbon pool, implying the importance of peat-derived organic matter in the coastal carbon cycle.

We surveyed the spatial and seasonal variations and estimated the seaward export of DOM in the of Pearl River estuary (PRE), China. The concentration of DOM in this estuary decreases from land to sea but the change in its chemical character is marginal. The concentration and export of DOM are the lowest among the world's major rivers. Yet DOM delivered from the PRE is protein-rich and can be readily used by microbes, thereby exerting a potentially important impact on the local marine ecosystem.

Nitrogen deposition and fertilizer can change how much carbon is stored in plants and soils. Understanding how much added nitrogen is recovered in plants or soils is critical to estimating the size of the future land carbon sink. We compared how nitrogen additions are recovered in modeled soil and plant stocks against data from long-term nitrogen addition experiments. We found that the model simulates recovery of added nitrogen into soils through a different process than found in the field.