Daily variability of dissolved inorganic radiocarbon in Sargasso Sea surface water

Abstract

Surface water samples were collected daily in June 2000 at a site in the Sargasso Sea to observe variability of Δ 14 C values in dissolved inorganic carbon (DIC). Temperature, salinity, DIC concentration, alkalinity, and δ 13 C and Δ 14 C values of DIC were measured in the samples. Ten Δ 14 C measurements averaged 81 ± 8‰ and had a range of 24‰ over the sixteen-day cruise. Δ 14 C values were more variable during the latter half of the cruise. Salinity and temperature measurements in the mixed layer throughout the cruise indicate that there were changes in water mass that occurred at our site. We conclude that the daily range of DIC Δ 14 C values in the surface ocean at our site is several times greater than the annual change in surface waters in the Sargasso Sea during the last two decades of the 20th century. This points to the importance of obtaining multiple measurements of the surface ocean to adequately define the true variability of DIC Δ 14 C measurements.

Daily variability of dissolved inorganic radiocarbon at three sites in the surface ocean

“…Temperature-salinity data from five CTD casts (on days 2, 7, 11, 14 and 16) in the upper 250 m revealed large shifts in salinity between 2 and 25 m depth on days 7, 11, 14 and 16. Temperature values below ∼20 m were 2-3°C warmer after day 7 (McDuffee and Druffel, 2007).…”

“…This means that 14 C will "remember" a mixing event from a storm, entraining colder, usually lower 14 C water for a longer time than will SST. Daily measurements of surface DIC Δ 14 C were reported previously for sites in the North central Pacific (NCP) and the Sargasso Sea (SS) (McDuffee and Druffel, 2007). The Δ…”

“…Daily measurements of chemical and physical parameters at the SS site indicated a change in water mass that was coincident with an increase in variability of Δ 14 C values (McDuffee and Druffel, 2007) half way through the cruise.…”

C-14 analysis of groundwater down to the millilitre level

“…Radiocarbon measurements of dissolved inorganic carbon (DIC) in water using accelerator mass spectroscopy (AMS) have a strong impact on our present understanding of oceanic circulation and water mass formation [1,2]. Accurate determination of groundwater residence times are required to understand hydrogeological systems and to assess the sustainable use of groundwater [3,4].…”

Variability of Dissolved Inorganic Radiocarbon at a Surface Site in the Northeast Pacific Ocean

“…Temporal variability of the reservoir age at a given location in the surface ocean has been studied using seasonal and monthly coral skeletons (Brown et al 1993;Guilderson et al 2000) and daily surface water samples collected at sea (McDuffee and Druffel 2007;Druffel and Griffin 2008). A reason to know the temporal variability of the reservoir age is to constrain the uncertainty in the initial 14 C signature of surface-derived carbon when calculating the residence times of carbon pools in the ocean.…”