A high-resolution, absolute-dated Holocene and deglacial Asian monsoon record from Dongge Cave, China

The carbon cycle of the coastal ocean is a dynamic component of the global carbon budget. But the diverse sources and sinks of carbon and their complex interactions in these waters remain poorly understood. Here we discuss the sources, exchanges and fates of carbon in the coastal ocean and how anthropogenic activities have altered the carbon cycle. Recent evidence suggests that the coastal ocean may have become a net sink for atmospheric carbon dioxide during post-industrial times. Continued human pressures in coastal zones will probably have an important impact on the future evolution of the coastal ocean's carbon budget.

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The changing carbon cycle of the coastal ocean

Thorium-230 ages and oxygen isotope ratios of stalagmites from Dongge Cave, China, characterize the Asian Monsoon and low-latitude precipitation over the past 160,000 years. Numerous abrupt changes in 18O/16O values result from changes in tropical and subtropical precipitation driven by insolation and millennial-scale circulation shifts. The Last Interglacial Monsoon lasted 9.7 +/- 1.1 thousand years, beginning with an abrupt (less than 200 years) drop in 18O/16O values 129.3 +/- 0.9 thousand years ago and ending with an abrupt (less than 300 years) rise in 18O/16O values 119.6 +/- 0.6 thousand years ago. The start coincides with insolation rise and measures of full interglacial conditions, indicating that insolation triggered the final rise to full interglacial conditions.

https://science.sciencemag.org/content/sci/304/5670/575.full.pdf

Timing, Duration, and Transitions of the Last Interglacial Asian Monsoon

Improvements in 230Th dating, 230Th and 234U half-life values, and U–Th isotopic measurements by multi-collector inductively coupled plasma mass spectrometry

The recent warming in the Arctic is affecting a broad spectrum of physical, ecological, and human/cultural systems that may be irreversible on century time scales and have the potential to cause rapid changes in the earth system. The response of the carbon cycle of the Arctic to changes in climate is a major issue of global concern, yet there has not been a comprehensive review of the status of the contemporary carbon cycle of the Arctic and its response to climate change. This review is designed to clarify key uncertainties and vulnerabilities in the response of the carbon cycle of the Arctic to ongoing climatic change. While it is clear that there are substantial stocks of carbon in the Arctic, there are also significant uncertainties associated with the magnitude of organic matter stocks contained in permafrost and the storage of methane hydrates beneath both subterranean and submerged permafrost of the Arctic. In the context of the global carbon cycle, this review demonstrates that the Arctic plays an important role in the global dynamics of both CO2 and CH4. Studies suggest that the Arctic has been a sink for atmospheric CO2 of between 0 and 0.8 Pg C/yr in recent decades, which is between 0% and 25% of the global net land/ocean flux during the 1990s. The Arctic is a substantial source of CH4 to the atmosphere (between 32 and 112 Tg CH4/yr), primarily because of the large area of wetlands throughout the region. Analyses to date indicate that the sensitivity of the carbon cycle of the Arctic during the remainder of the 21st century is highly uncertain. To improve the capability to assess the sensitivity of the carbon cycle of the Arctic to projected climate change, we recommend that (1) integrated regional studies be conducted to link observations of carbon dynamics to the processes that are likely to influence those dynamics, and (2) the understanding gained from these integrated studies be incorporated into both uncoupled and fully coupled carbon-climate modeling efforts. (Less)

/pdf/sensitivity-of-the-carbon-cycle-in-the-arctic-to-climate-1k0jtzf35t.pdf

Sensitivity of the carbon cycle in the Arctic to climate change

Uranium and thorium isotopic and concentration measurements by magnetic sector inductively coupled plasma mass spectrometry

A technique has been developed to quantify ultratrace 231Pa (50−2000 ag; 1 ag = 10-18 g) concentrations in seawater using isotope-dilution thermal ionization mass spectrometry (TIMS). The method is a modification of a process developed by Pickett et al. (Pickett, D. A.; Murrell, M. T.; Williams, R. W. Anal. Chem. 1994, 66, 1044−1049) and extends the technique to very low levels of protactinium. The procedural blank is 16 ± 15 ag (2σ), and the ionization efficiency (ions generated/atom loaded) approaches 0.5%. Measurement time is <1 h. The amount of 231Pa needed to produce 231Pa data with an uncertainty of ±4−12% is 100−1000 ag (∼3 × 105 to 3 × 106 atoms). Replicate measurements made on known standards and seawater samples demonstrate that the analytical precision approximates that expected from counting statistics and that, based on detection limits of 38 and 49 ag, protactinium can be detected in a minimum sample size of surface seawater of ∼2 L for suspended particulate matter and <0.1 L for filtered (<...

Measurement of attogram quantities of 231Pa in dissolved and particulate fractions of seawater by isotope dilution thermal ionization mass spectroscopy.

[1] The Arctic Ocean and adjacent continental shelf seas such as the Chukchi and Beaufort Seas are particularly sensitive to long-term change and low-frequency modes of atmosphere-ocean-sea-ice forcing. The cold, low salinity surface waters of the Canada Basin of the Arctic Ocean are undersaturated with respect to CO2 in the atmosphere and the region has the potential to take up atmospheric CO2, although presently suppressed by sea-ice cover. Undersaturated seawater CO2 conditions of the Arctic Ocean are maintained by export of water with low dissolved inorganic carbon content and modified by intense seasonal shelf primary production. Sea-ice extent and volume in the Arctic Ocean has decreased over the last few decades, and we estimate that the Arctic Ocean sink for CO2 has tripled over the last 3 decades (24 Tg yr 1 to 66 Tg yr 1 ) due to sea-ice retreat with future sea-ice melting enhancing air-to-sea CO2 flux by 28% per decade. Citation: Bates, N. R., S. B. Moran, D. A. Hansell, and J. T. Mathis (2006), An increasing CO2 sink in the Arctic Ocean due to sea-ice loss, Geophys. Res. Lett., 33, L23609, doi:10.1029/2006GL027028.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006GL027028

An increasing CO2 sink in the Arctic Ocean due to sea‐ice loss

Size-fractionated 234 Th in continental shelf waters off New England: Implications for the role of colloids in oceanic trace metal scavenging

Profiles of particulate and dissolved 234 Th ( t 1/2 =24.1 d) were collected during the Canadian JGOFS program (February, May, and August 1996 and February 1997) along a transect from 125°W to 145°W at 50°N (Ocean Station Papa – OSP). Persistent features included a deficit of 234 Th relative to its parent 238 U in the upper ∼75 m and occasionally an excess of total 234 Th (particulate+dissolved) at ∼150–200 m attributed to redissolution of the particulate-bound nuclide. To calculate POC export fluxes, a steady-state model of 234 Th export was combined with measurements of the POC/ 234 Th ratio determined on particles >1-μm collected by in situ filtration. Along the transect, e-ratios (POC export/primary production) calculated for the 0.1% light level were similar during February 1997 and May 1996, 0.06–0.08 (avg. POC flux =2.8–7.1 mmol C m −2  d −1 ). During August 1996, e-ratio s reached a maximum, averaging 0.13 (avg. POC flux=7.6 mmol C m −2  d −1 ). Particulate 234 Th fluxes measured by drifting cylindrical sediment traps were 3-fold greater than the flux calculated for the water column 234 Th deficit. Finally, to study changes in 234 Th and POC export on short time-scales, some stations were sampled twice within 36 hours. During February 1997, 234 Th increased nearly 50% from 60–100 m in a 36 h period. Hydrographic data suggest that this change was due to advective processes.

S. Bradley Moran

Papers

Uranium and thorium isotopic and concentration measurements by magnetic sector inductively coupled plasma mass spectrometry

Measurement of attogram quantities of 231Pa in dissolved and particulate fractions of seawater by isotope dilution thermal ionization mass spectroscopy.

An increasing CO2 sink in the Arctic Ocean due to sea‐ice loss

Size-fractionated 234 Th in continental shelf waters off New England: Implications for the role of colloids in oceanic trace metal scavenging

as a tracer of particulate organic carbon export in the subarctic northeast Pacific Ocean