Low-latitude mesopelagic nutrient recycling controls productivity and export.

Low-latitude (LL) oceans account for up to half of global net primary production and export. It has been argued that the Southern Ocean dominates LL primary production and export, with implications for the response of global primary production and export to climate change. Here we applied observational analyses and sensitivity studies to an individual model to show, instead, that 72% of LL primary production and 55% of export is controlled by local mesopelagic macronutrient cycling.

India's Riverine Nitrogen Runoff Strongly Impacted by Monsoon Variability.

Agricultural intensification in India has increased nitrogen pollution, leading to water quality impairments. The fate of reactive nitrogen applied to the land is largely unknown, however. Long-term records of riverine nitrogen fluxes are nonexistent and drivers of variability remain unexamined, limiting the development of nitrogen management strategies.

The land-to-ocean loops of the global carbon cycle.

Carbon storage by the ocean and by the land is usually quantified separately, and does not fully take into account the land-to-ocean transport of carbon through inland waters, estuaries, tidal wetlands and continental shelf waters-the 'land-to-ocean aquatic continuum' (LOAC). Here we assess LOAC carbon cycling before the industrial period and perturbed by direct human interventions, including climate change. In our view of the global carbon cycle, the traditional 'long-range loop', which carries carbon from terrestrial ecosystems to the open ocean through rivers, is reinforced by two 'short-range loops' that carry carbon from terrestrial ecosystems to inland waters and from tidal wetlands to the open ocean.

Reassessing Southern Ocean Air-Sea CO Flux Estimates With the Addition of Biogeochemical Float Observations.

New estimates of CO from profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project have demonstrated the importance of wintertime outgassing south of the Polar Front, challenging the accepted magnitude of Southern Ocean carbon uptake (Gray et al., 2018, https://doi:10.1029/2018GL078013).

Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis.

A decrease in the C/C ratio of atmospheric CO has been documented by direct observations since 1978 and from ice core measurements since the industrial revolution. This decrease, known as the C-Suess effect, is driven primarily by the input of fossil fuel-derived CO but is also sensitive to land and ocean carbon cycling and uptake. Using updated records, we show that no plausible combination of sources and sinks of CO from fossil fuel, land, and oceans can explain the observed C-Suess effect unless an increase has occurred in the C/C isotopic discrimination of land photosynthesis.

Decadal acidification in the water masses of the Atlantic Ocean.

Global ocean acidification is caused primarily by the ocean's uptake of CO2 as a consequence of increasing atmospheric CO2 levels. We present observations of the oceanic decrease in pH at the basin scale (50 °S-36 °N) for the Atlantic Ocean over two decades (1993-2013). Changes in pH associated with the uptake of anthropogenic CO2 (ΔpHCant) and with variations caused by biological activity and ocean circulation (ΔpHNat) are evaluated for different water masses.