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The Southern Ocean regulates atmospheric CO2 and Earth's climate as a critical region for air‐sea gas exchange, delicately poised between being a CO2 source and sink. Here, we estimate how long a water mass has remained isolated from the atmosphere and utilize 14C/12C ratios (Δ14C) to trace the pathway and escape route of carbon sequestered in the deep ocean through the mixed layer to the atmosphere. The position of our core at the northern margin of the Southern Indian Ocean, tracks latitudinal shifts of the Southern Ocean frontal zones across the deglaciation. Our results suggest an expanded glacial Antarctic region trapped CO2, whereas deglacial expansion of the subantarctic permitted ventilation of the trapped CO2, contributing to a rapid atmospheric CO2 rise. We identify frontal positions as a key factor balancing CO2 outgassing versus sequestration in a region currently responsible for nearly half of global ocean CO2 uptake. Plain Language Summary: The Southern Ocean is a key region for the inhalation and exhalation of carbon dioxide, responsible for absorbing nearly half of the total amount of atmospheric c taken up by the modern global ocean. Today, regions of communication between the deep ocean and atmosphere are bounded by oceanographic fronts. During cold glacial periods, when sea ice cover expanded in the Southern Ocean, these regions were shifted northward. Our data shows that this northward movement pinched together the fronts in the Southern Indian Ocean, restricting glacial ocean‐atmosphere gas exchange, allowing CO2 to accumulate in the deep ocean. We find that at the end of the glaciation, the fronts returned southward and expanded, allowing transfer of the stored CO2 into intermediate and surface waters before escaping to the atmosphere. This trapping and releasing mechanism driven by frontal shifts is important for understanding how changes in Southern Ocean dynamics can affect the ability of the oceans to take up the additional atmospheric CO2 produced from human activities. Key Points: Indian Ocean Antarctic Intermediate Water was a pathway for ventilation of a deglacial carbon reservoirLatitudinal shifts in the Southern Ocean fronts contributed to glacial carbon storage and deglacial ventilationIntermediate waters of the Southern Indian Ocean were more than 2,000 years older in the deglaciation than the glacial and Holocene [ABSTRACT FROM AUTHOR]

Primary and secondary standards are essential in radiocarbon analyses for the purpose of reporting and comparing data among laboratories, as well as for internal laboratory data quality control. ANU sucrose is one of the IAEA-certified 14C standards (C-6) with a consensus value of 1.5061 ± 0.0011 fraction modern (Fm). All of our measurements of ANU sucrose (n = 351) as a secondary standard over the last 7 yr result in an average value of 1.5016 ± 0.0005 Fm (2-σ standard error). After applying the same outlier tests used for IAEA reference standards, a weighted average value of 1.5016 ± 0.0002 Fm (n = 294) was calculated. This value is significantly lower than the IAEA C-6 consensus value (t test with unequal variance; p = 0.023). In contrast, our measurements of other secondary standards over the same time period are in excellent agreement with their respective consensus values. Since ANU is the only secondary standard measured in our lab that does not agree with the consensus values, and we have measured a larger number analyses compared to what went into the definition of the consensus value, we suggest that the consensus value of ANU sucrose might be too high by ~0.0045 ± 0.0011 Fm. Given that some labs routinely use ANU sucrose as a primary standard, our results suggest that revisiting the consensus value of ANU sucrose may be necessary.

Methane (CH4) in the subsurface ocean is often supersaturated compared to equilibrium with the modern atmosphere. In order to investigate sources of CH4 to the subsurface ocean, isotope surveys (14C-CH4, δ13 C-CH4, δ2 H-CH4) were conducted at five locations: Skan Bay (SB), Santa Barbara Basin (SBB), Santa Monica Basin (SMB), Cariaco Basin (CB), and the Guaymas Basin (GB). Depth distributions of CH4 concentration and isotopic abundance were determined for both the sediment and water column at the SB, SBB, SMB, and CB sites; CH4 emitted from seeps on the continental shelf adjacent to the SBB as well as seeps and decomposing clathrate hydrates in the GB was also collected, purified, and analyzed. Methane isotope distributions in the sediments were consistent with known methanogenic and methanotrophic activity; seep- and clathrate-hydrate-derived CH4 was found to be depleted in radiocarbon. However, surprising results were obtained in the water column at all sites investigated. In SB the radiocarbon content of the subsurface CH4 concentration maximum was on average 41% less than its suspected sediment CH4 source, suggesting CH4 seepage in the bay. In the SBB, SMB, and CB, the 14C-CH4 contents in the subsurface ocean were 1.2 to 3.6 times greater than modem carbon quantities suggesting a source of 14C from atmospheric nuclear weapons testing, nuclear power plant effluents, or cosmogenic isotope production. Copyright 2008 by the American Geophysical Union.

Numerous methane-emitting bottom features, such as seeps, methane clathrate hydrates (clathrates), and mud volcanoes, have been identified recently in the Black Sea. The fluxes of methane from these sources averaged over large spatial scales are unknown. Here we take advantage of the fact that the Black Sea is a semi-enclosed basin with restricted deep water circulation to establish first-order estimates of basin-wide fluxes of methane from these sources to the water column and atmosphere. First, we measured the natural radiocarbon content of methane (14C-CH4) dissolved in the water column and emitted from seeps. The 14C-CH4 results showed that the dominant source of methane to the water column is emitted from seeps and a smaller source is diagenetically produced in relatively modern sediments. The 14C-CH4 results were then used to partition a basin-wide total methane budget; this analysis estimated the basin-wide flux of methane from seeps and clathrates to the water column to be 3.60 to 4.28 Tg yr-1. Second, a geochemical box model was used to calculate possible distributions of methane inputs from seeps and clathrates as well as provide additional estimates of the basin-wide flux of methane from seeps and clathrates to the water column (4.95 to 5.65 Tg yr-1). © 2006 Elsevier B.V. All rights reserved.

Natural radiocarbon measurements on methane (14C-CH4) extracted from the Cariaco Basin water column show that 98% of the methane in Cariaco Basin waters is derived from fossil (radiocarbon-free) sources. Previous work on Cariaco Basin methane (CH4) considered only a diagenetic sediment source. Similar measurements of sediment 14C-CH4 indicate that sediment CH4 is produced from modern particulate material; thus the sediment and water column CH4 have distinct sources. Using time-dependent CH4 geochemical box models which include a fossil seep CH4 source term, we estimate 1) 0.024-0.028 Tg y-1 of seep CH4 are added to the Cariaco Basin water column, 2) the water column CH4 will reach a steady-state concentration by the year 2065, and 3) the seep CH4 inputs possibly began in 1967, following the July 30 Caracas earthquake. Oxidizing this CH4 to dissolved inorganic carbon does not appear to affect Cariaco Basin 14C chronologies. Copyright 2005 by the American Geophysical Union.

The costs of Accelerator Mass Spectrometry (AMS) systems for radiocarbon measurementshave dropped sharply in recent years, but at $1M to $1.3M, these instruments still represent majorinvestments. However, these costs are not excessive for a facility producing several thousand highprecision 14C analyses per year. Here we describe methods developed at the AMS laboratory atUniversity of California Irvine (UC Irvine) for achieving high throughput at high precision. Key factorsinclude: large-scale parallelism in sample preparation plus streamlining of sample pretreatmentprocedures; development of a robust and easily maintainable high output ion source; removal of dataanalysis bottlenecks; and training of laboratory personnel to ensure that several staff members can carryout critical functions.

On a sequence of soils developed under similar vegetation, temperature, and precipitation conditions, but with variations in mineralogical properties, we use organic carbon and 14C inventories to examine mineral protection of soil organic carbon. In these soils, 14C data indicate that the creation of slow-cycling carbon can be modeled as occurring through reaction of organic ligands with Al3+ and Fe3+ cations in the upper horizons, followed by sorption to amorphous inorganic Al compounds at depth. Only one of these processes, the chelation of Al3+ and Fe3+ by organic ligands, is linked to large carbon stocks. Organic ligands stabilized by this process traverse the soil column as dissolved organic carbon (both from surface horizons and root exudates). At our moist grassland site, this chelation and transport process is very strongly correlated with the storage and long-term stabilization of soil organic carbon. Our 14C results show that the mechanisms of organic carbon transport and storage at this site follow a classic model previously believed to only be significant in a single soil order (Spodosols), and closely related to the presence of forests. The presence of this process in the grassland Alfisol, Inceptisol, and Mollisol soils of this chronosequence suggests that this process is a more significant control on organic carbon storage than previously thought.

On a sequence of soils developed under similar vegetation, temperature, and precipitation conditions, but with variations in mineralogical properties, we use organic carbon and 14C inventories to examine mineral protection of soil organic carbon. In these soils, 14C data indicate that the creation of slow-cycling carbon can be modeled as occurring through reaction of organic ligands with Al3+ and Fe3+ cations in the upper horizons, followed by sorption to amorphous inorganic Al compounds at depth. Only one of these processes, the chelation of Al3+ and Fe3+ by organic ligands, is linked to large carbon stocks. Organic ligands stabilized by this process traverse the soil column as dissolved organic carbon (both from surface horizons and root exudates). At our moist grassland site, this chelation and transport process is very strongly correlated with the storage and long-term stabilization of soil organic carbon. Our 14C results show that the mechanisms of organic carbon transport and storage at this site follow a classic model previously believed to only be significant in a single soil order (Spodosols), and closely related to the presence of forests. The presence of this process in the grassland Alfisol, Inceptisol, and Mollisol soils of this chronosequence suggests that this process is a more significant control on organic carbon storage than previously thought.

. Radiocarbon (∆14C) measurements of monthly samples from a Galapagos surface coral are among the firstdata sets from the new Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of California, Irvine.An average ∆14C value of –62‰ is obtained for 144 measurements of samples from monthly coral bands that lived fromabout AD 1760–1771 (±6 yr). High ∆14C values were found during January through March, when upwelling was weak orabsent at the Galapagos Islands. Low ∆14C values were obtained mid-year during strong upwelling. The average seasonalvariability of ∆14C was 15–25‰, which is greater than that at other tropical and subtropical locations in the Pacific Oceanbecause of intense seasonal upwelling at this site. Periods of sustained high ∆14C values were found during 1762–1763 and1766. A spectral analysis revealed that the spectral density for the ∆14C data displays most of its variance at the 5-yr cycle,which is reflective of El Niño periodicity during the 20th century.

A new radiocarbon accelerator mass spectrometry (AMS) laboratory for carbon cycle studies has been established at the University of California, Irvine. The 0.5MV AMS system was installed in mid-2002 and has operated routinely since October of that year. This paper briefly describes the spectrometer and summarizes lessons learned during the first year of operation. In the process of setting up the system, we identified and largely suppressed a previously unreported C-14 AMS background: charge exchange tails from N-14 beams derived from nitrogen-containing molecular ions produced near the entrance of the accelerator.

We show that high-precision radiocarbon (Δ14C) measurements from annual bands of a Hawaiian surface coral decreased by 7‰ from AD 1893 to 1952. This decrease is coincident with the Suess Effect, which is mostly due to the dilution of natural levels of 14C by 14C-free fossil fuel CO2. This decrease is equal to that expected in surface waters of the subtropical gyres, and indicates that the surface waters of the North Pacific were in steady state with respect to long term mixing of CO2 during the past century. Correlation between Δ14C and North Pacific gyre sea surface temperatures indicates that vertical mixing local to Hawaii and the North Pacific gyre as a whole is the likely physical mechanism to result in variable Δ14C. Prior to 1920, this correlation starts to break down; this may be related to the non-correlation between biennial Δ14C values in corals from the southwest Pacific and El Niño events observed during this period as well.

Previous work has suggested that apparent old 14C ages for oceanic DOC are the result of mixing of different organic carbon fractions. This report provides direct evidence for a contemporary 14C age of a high-molecular-weight (HMW) fraction of colloidal organic carbon (≥10 kD). Colloidal organic matter, COM10 (from 10 kDaltons (kD) to 0.2 μm), isolated from the upper water column of the Gulf of Mexico and the Middle Atlantic Bight (MAB) region, generally has a contemporary age (i.e., younger than a few decades), while COM1 (from 1 kD to 0.2 μm), is apparently old: 380-4500 y bP. Thus, BMW COM10 (3-5% of DOC) from the upper water column is derived from living particulate organic matter (POM) and cycles rapidly, while a significant fraction of low-molecular-weight (≤1 kD) DOM is likely more refractory, and cycles on much longer time scales. The presence of pigment biomarker compounds in COM1 from the upper water column points to selected phytoplankton species as one of the sources of COM. Terrestrial carbon as another source of COM is suggested from the inverse correlation between Δ14C and δ13C values, as well as the increasing δ13C values with increasing salinity. 234Th-derived turnover times of COM10 and COM1 from both the Gulf of Mexico and MAB are consistently short, 1-20 and 3-30 days, respectively. These short residence times support the hypothesis that 14C ages of colloidal fractions of DOC are the result of COM fractions being a mixture of several endmembers with fast and slow turnover rates. © 1995.

We measured carbon isotope abundances in the layered, proteinaceous skeleton of a zoanthid Gerardia collected from 620 m depth off the Little Bahama Bank (27°N, 79°W). The δ 14C values decreased from -76% in the outer growth edge to an average of -267% in the center of three portions of the skeleton. These δ 14C data suggest an age for this living organism of 1800 ± 300 years. The possibility that the large decrease in δ 14C reflects the gradual input of bomb 14C over the entire growth of the organism is inconsistent with the post-bomb δ 14C values obtained for the most recent growth tips. If the age estimate of two millennia is correct, it may be the longest-lived animal yet observed in the ocean. Gerardia may serve as a long-lived recorder of ocean chemistry, similar to the Bristlecone pine tree that has served as a millennial-timescale recorder for atmospheric 14CO2 (Suess, 1980) and climate. In particular, there is potential for Gerardia to serve as a millennial-scale integrator of upper ocean particle flux, and possibly reveal past changes in the productivity of the surface ocean. © 1995.

Radiocarbon age may deviate significantly from calendar age as a result of time-varying processes affecting [sup.14]C production in the atmosphere, as well as the distribution of [sup.14]C among the active [...], A series of [sup.14]C measurements in Ocean Drilling Program cores from the tropical Cariaco Basin, which have been correlated to the annual-layer counted chronology for the Greenland Ice Sheet Project 2 (GISP2) ice core, provides a high-resolution calibration of the radiocarbon time scale back to 50,000 years before the present. Independent radiometric dating of events correlated to GISP2 suggests that the calibration is accurate. Reconstructed [sup.14]C activities varied substantially during the last glacial period, including sharp peaks synchronous with the Laschamp and Hone Lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments. Simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in [sup.14]C production rate together with plausible changes in deep-ocean ventilation and the global carbon cycle during glaciation.

Abrupt climate fluctuations during the Holocene and Late Pleistocene times have been associated with change in ocean circulation, although their causes remains uncertain. A major cooling event in the Holocene occurred between 8,400 and 8,000 years ago in central Greenland and around the north eastern North Atlantic Ocean. It is argued that the event was due to a massive outflow of fresh water from the Hudson Strait based on estimates of the marine reservoir for Hudson Bay. This lends support to the hypothesis that the sudden rise in freshwater flux from the waning Laurentide ice sheet lessened sea surface salinity and altered ocean circulation.

On 4 July AD 1054 a supernova brighter than Venus appeared in the sky, remaining visible for approximately 23 days and 650 nights. It was chronicled in five independent historic [...]