Distribution profiles of radiocarbon in dissolved inorganic carbonate have been measured along two transects in the southern Pacific, east of New Zealand. Use of accelerator mass spectrometry, with its small-sample-size capability, made it possible to sample near-surface waters with a depth resolution of a few tens of meters. Sampling of deeper water was guided by salinity and temperature data transmitted by a conductivity-temperature-depth probe. The measurements, taken over the Chatham Rise, show highly structured profiles that can be correlated with known circulation patterns in this region.
We develop a high precision Δ 14 CO 2 measurement capability in 2‐5 L samples of whole air for implementation within existing greenhouse gas flask sampling networks. The long‐term repeatability of the measurement is 1.8‰ (1‐sigma), as determined from repeated analyses of quality control standards and replicate extraction and measurement of authentic field samples. In a parallel effort, we have begun a Δ 14 CO 2 measurement series from NOAA/ESRL’s (formerly NOAA/CMDL) surface flask sampling site at Niwot Ridge, Colorado, USA (40.05°N, 105.58°W, 3475 masl) in order to monitor the isotopic composition of carbon dioxide in relatively clean air over the North American continent. Δ 14 CO 2 at Niwot Ridge decreased by 5.7‰/yr from 2004 to 2006, with a seasonal amplitude of 3‐5‰. A comparison with measurements from the free troposphere above New England, USA (41°N, 72°W) indicates that the Δ 14 CO 2 series at the two sites are statistically similar at timescales longer than a few days to weeks (i.e., those of synoptic scale variations in transport), suggesting that the Niwot Ridge measurements can be used as a proxy for North American free tropospheric air in future carbon cycle studies.
An isotopic database for the Pacific/Polynesian rat ( Rattus exulans ) and foods that it scavenges is used to examine diet-induced 14 C age variation in omnivores. We discuss a suite of 26 δ 14 C determinations and 13 C and 15 N analysis for modern Pacific/Polynesian rat bone gelatin and available food items from Kapiti Island, New Zealand (40°51'S, 174°75'E). These analyses provide the first isotopic data for modern specimens of the species, collected as part of a larger project to determine potential sources of bias in unexpectedly old 14 C age measurements on subfossil specimens of R. exulans from New Zealand. Stable C, N and 14 C isotopic and trapping data are used to trace carbon intake via the diet of the rats in each habitat. Data from specimens linked to five specific habitats on the island indicate that modern populations of R. exulans are not in equilibrium with atmospheric values of δ 14 C, being either enriched or depleted relative to the atmospheric curve in 1996/97, the period of collection. The δ 14 C values recorded for R. exulans are associated with diet, and result from variation in δ 14 C values found in animal-protein food items available to a scavenging omnivore. The titer of carbon deviating from atmospheric values is believed to be derived from the essential amino acids in the protein-rich foods of the rat diet. Present evidence suggests that the depletion required to affect 14 C ages limits the possibility that diet introduces dramatic offsets from true ages. Marine diets, for example, would have a variable effect on ages for terrestrial omnivores, contraindicating the application of a standard marine correction for such specimens. We suggest that to identify the extent to which diet may influence the 14 C age in a given specimen of terrestrial omnivore, the separation and dating of essential amino acids vs. a nonessential amino, such as glycine, be applied.
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The 2,500‐km Kermadec‐Tonga arc is the longest submarine arc on the planet. Here, we report on the second of a series of cruises designed to investigate large‐scale controls on active hydrothermal venting on this arc. The 2002 NZAPLUME II cruise surveyed 12 submarine volcanic centers along ∼580 km of the middle Kermadec arc (MKA), extending a 1999 cruise that surveyed 260 km of the southern Kermadec arc (SKA). Average spacing between volcanic centers increases northward from 30 km on backarc crust along the SKA, to 45 km on backarc crust along the southern MKA, to 58 km where the MKA joins the Kermadec Ridge. Volcanic cones dominate in the backarc, and calderas dominate the Kermadec Ridge. The incidence of venting is higher along the MKA (83%, 10 of 12 volcanic centers) than the SKA (67%, 8 of 12), but the relative intensity of venting, as given by plume thickness, areal extent, and concentration of dissolved gases and ionic species, is generally weaker in the MKA. This pattern may reflect subduction of the ∼17‐km‐thick oceanic Hikurangi Plateau beneath the SKA. Subduction of this basaltic mass should greatly increase fluid loss from the downgoing slab, initiating extensive melting in the upper mantle wedge and invigorating the hydrothermal systems of the SKA. Conversely, volcanic centers in the southern MKA are starved of magma replenishment and so their hydrothermal systems are waning. Farther north, where the MKA centers merge with the Kermadec Ridge, fewer but larger magma bodies accumulate in the thicker (older) crust, ensuring more widely separated, caldera‐dominated volcanic centers.
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