More Like this

1. The flower garden banks Siderastrea siderea coral as a candidate global boundary stratotype section and point for the Anthropocene series

   https://doi.org/10.1177/20530196221147616  

   DeLong, Kristine L. ; Palmer, Kylie ; Wagner, Amy J. ; Weerabaddana, Mudith M. ; Slowey, Niall ; Herrmann, Achim D. ; Duprey, Nicolas ; Martínez-García, Alfredo ; Jung, Jonathan ; Hajdas, Irka ; et al ( February 2023 , The Anthropocene Review)

   The proposed Anthropocene Global Boundary Stratotype Section and Point (GSSP) candidate site of West Flower Garden Bank (27.8762°N, 93.8147°W) is an open ocean location in the Gulf of Mexico with a submerged coral reef and few direct human impacts. Corals contain highly accurate and precise (<±1 year) internal chronologies, similar to tree rings, and their exoskeletons are formed of aragonite and can be preserved in the rock record. Here we present results from a large Siderastrea siderea coral (core 05WFGB3; 1755–2005 CE) sampled with annual and monthly resolutions that show clear markers of global and regional human impacts. Atmospheric nuclear bomb testing by-products (¹⁴C,^239+240Pu) have clear increases in this coral starting in 1957 for¹⁴C and the first increase in 1956 for^239+240Pu (potential bases for the Anthropocene GSSP). Coral δ¹³C declined especially after 1956 consistent with the Suess Effect resulting from the burning of fossil fuels. Coral skeletal δ¹⁵N starts to increase in 1963 corresponding with the increase in agricultural fertilizers. Coral Hg concentrations (1933–1980) loosely track fluctuations in industrial pollution and coral Ba/Ca increases from 1965–1983 when offshore oil operations expand after 1947. Coral temperature proxies contain the 20th-century global warming trend whereas coral growth declines during this interval.

    

   more » « less
2. Increased Terrestrial Carbon Export and CO 2 Evasion From Global Inland Waters Since the Preindustrial Era

   https://doi.org/10.1029/2023GB007776  

   Tian, Hanqin ; Yao, Yuanzhi ; Li, Ya ; Shi, Hao ; Pan, Shufen ; Najjar, Raymond G. ; Pan, Naiqing ; Bian, Zihao ; Ciais, Philippe ; Cai, Wei‐Jun ; et al ( October 2023 , Global Biogeochemical Cycles)

   Global carbon dioxide (CO₂) evasion from inland waters (rivers, lakes, and reservoirs) and carbon (C) export from land to oceans constitute critical terms in the global C budget. However, the magnitudes, spatiotemporal patterns, and underlying mechanisms of these fluxes are poorly constrained. Here, we used a coupled terrestrial–aquatic model to assess how multiple changes in climate, land use, atmospheric CO₂concentration, nitrogen (N) deposition, N fertilizer and manure applications have affected global CO₂evasion and riverine C export along the terrestrial‐aquatic continuum. We estimate that terrestrial C loadings, riverine C export, and CO₂evasion in the preindustrial period (1800s) were 1,820 ± 507 (mean ± standard deviation), 765 ± 132, and 841 ± 190 Tg C yr⁻¹, respectively. During 1800–2019, multifactorial global changes caused an increase of 25% (461 Tg C yr⁻¹) in terrestrial C loadings, reaching 2,281 Tg C yr⁻¹in the 2010s, with 23% (104 Tg C yr⁻¹) of this increase exported to the ocean and 59% (273 Tg C yr⁻¹) being emitted to the atmosphere. Our results showed that global inland water recycles and exports nearly half of the net land C sink into the atmosphere and oceans, highlighting the important role of inland waters in the global C balance, an amount that should be taken into account in future C budgets. Our analysis supports the view that a major feature of the global C cycle–the transfer from land to ocean–has undergone a dramatic change over the last two centuries as a result of human activities.

    

   more » « less
3. How Well Do We Understand the Land‐Ocean‐Atmosphere Carbon Cycle?

   https://doi.org/10.1029/2021RG000736  

   Crisp, David ; Dolman, Han ; Tanhua, Toste ; McKinley, Galen A. ; Hauck, Judith ; Bastos, Ana ; Sitch, Stephen ; Eggleston, Simon ; Aich, Valentin ( May 2022 , Reviews of Geophysics)

   Fossil fuel combustion, land use change and other human activities have increased the atmospheric carbon dioxide (CO₂) abundance by about 50% since the beginning of the industrial age. The atmospheric CO₂growth rates would have been much larger if natural sinks in the land biosphere and ocean had not removed over half of this anthropogenic CO₂. As these CO₂emissions grew, uptake by the ocean increased in response to increases in atmospheric CO₂partial pressure (pCO₂). On land, gross primary production also increased, but the dynamics of other key aspects of the land carbon cycle varied regionally. Over the past three decades, CO₂uptake by intact tropical humid forests declined, but these changes are offset by increased uptake across mid‐ and high‐latitudes. While there have been substantial improvements in our ability to study the carbon cycle, measurement and modeling gaps still limit our understanding of the processes driving its evolution. Continued ship‐based observations combined with expanded deployments of autonomous platforms are needed to quantify ocean‐atmosphere fluxes and interior ocean carbon storage on policy‐relevant spatial and temporal scales. There is also an urgent need for more comprehensive measurements of stocks, fluxes and atmospheric CO₂in humid tropical forests and across the Arctic and boreal regions, which are experiencing rapid change. Here, we review our understanding of the atmosphere, ocean, and land carbon cycles and their interactions, identify emerging measurement and modeling capabilities and gaps and the need for a sustainable, operational framework to ensure a scientific basis for carbon management.

    

   more » « less
4. Atmosphere‐Ocean CO 2 Exchange Across the Last Deglaciation From the Boron Isotope Proxy

   https://doi.org/10.1029/2018PA003498  

   Shao, Jun ; Stott, Lowell D. ; Gray, William R. ; Greenop, Rosanna ; Pecher, Ingo ; Neil, Helen L. ; Coffin, Richard B. ; Davy, Bryan ; Rae, James W. B. ( October 2019 , Paleoceanography and Paleoclimatology)

   Identifying processes within the Earth System that have modulated atmospheric pCO₂during each glacial cycle of the late Pleistocene stands as one of the grand challenges in climate science. The growing array of surface ocean pH estimates from the boron isotope proxy across the last glacial termination may reveal regions of the ocean that influenced the timing and magnitude of pCO₂rise. Here we present two new boron isotope records from the subtropical‐subpolar transition zone of the Southwest Pacific that span the last 20 kyr, as well as new radiocarbon data from the same cores. The new data suggest this region was a source of carbon to the atmosphere rather than a moderate sink as it is today. Significantly higher outgassing is observed between ~16.5 and 14 kyr BP, associated with increasing δ¹³C and [CO₃]²⁻at depth, suggesting loss of carbon from the intermediate ocean to the atmosphere. We use these new boron isotope records together with existing records to build a composite pH/pCO₂curve for the surface oceans. The pH disequilibrium/CO₂outgassing was widespread throughout the last deglaciation, likely explained by upwelling of CO₂from the deep/intermediate ocean. During the Holocene, a smaller outgassing peak is observed at a time of relatively stable atmospheric CO₂, which may be explained by regrowth of the terrestrial biosphere countering ocean CO₂release. Our stack is likely biased toward upwelling/CO₂source regions. Nevertheless, the composite pCO₂curve provides robust evidence that various parts of the ocean were releasing CO₂to the atmosphere over the last 25 kyr.

    

   more » « less
5. Multiple carbon cycle mechanisms associated with the glaciation of Marine Isotope Stage 4

   https://doi.org/10.1038/s41467-022-33166-3  

   Menking, James A. ; Shackleton, Sarah A. ; Bauska, Thomas K. ; Buffen, Aron M. ; Brook, Edward J. ; Barker, Stephen ; Severinghaus, Jeffrey P. ; Dyonisius, Michael N. ; Petrenko, Vasilii V. ( September 2022 , Nature Communications)

   Here we use high-precision carbon isotope data (δ¹³C-CO₂) to show atmospheric CO₂during Marine Isotope Stage 4 (MIS 4, ~70.5-59 ka) was controlled by a succession of millennial-scale processes. Enriched δ¹³C-CO₂during peak glaciation suggests increased ocean carbon storage. Variations in δ¹³C-CO₂in early MIS 4 suggest multiple processes were active during CO₂drawdown, potentially including decreased land carbon and decreased Southern Ocean air-sea gas exchange superposed on increased ocean carbon storage. CO₂remained low during MIS 4 while δ¹³C-CO₂fluctuations suggest changes in Southern Ocean and North Atlantic air-sea gas exchange. A 7 ppm increase in CO₂at the onset of Dansgaard-Oeschger event 19 (72.1 ka) and 27 ppm increase in CO₂during late MIS 4 (Heinrich Stadial 6, ~63.5-60 ka) involved additions of isotopically light carbon to the atmosphere. The terrestrial biosphere and Southern Ocean air-sea gas exchange are possible sources, with the latter event also involving decreased ocean carbon storage.

    

   more » « less