Reduced scavenging of in the Weddell Sea: implications for paleoceanographic reconstructions in the South Atlantic

Earth and Planetary Science Letters

Kubik

Mangini

2002

Self Cite

We present the first transect of dissolved 10 Be depth profiles across the Antarctic Circumpolar Current (ACC) in the Atlantic sector. North of the Polar Front the 10 Be concentrations increase continuously from very low values at the surface to values of up to 1600 atoms/g at depth. Deep water 10 Be concentrations of particular water masses are consistent with earlier results obtained further north. South of the Polar Front and in the Weddell Sea the distribution of 10 Be is also characterised by low surface concentrations but below 1000 m depth the concentrations are relatively constant and significantly higher (up to 2000 atoms/g) than further north, probably as a result of mixing and advection of water masses of Pacific origin. Overall the deep water 10 Be distribution is obviously not significantly affected by scavenging processes or ice melt and comparison with the density distribution suggests that 10 Be can be viewed as a quasi-conservative tracer. This provides a tool for an improved understanding of the behaviour of other more particle reactive trace metals in the Southern Ocean such as 230 Th: in deep waters north of the ACC/Weddell Gyre boundary (AWB) 10 Be/ 230 Th has a relatively constant value (1.7 þ 0.3U10 9 atoms/dpm) over a wide density range whereas south of the AWB the ratio is significantly lower (1.1 þ 0.2U10 9 atoms/dpm). This normalisation to 10 Be corroborates that 230 Th is enriched by 50% due to accumulation south of the AWB as a consequence of minimal particulate fluxes. The quasi-conservative behaviour deduced from our results also implies that 10 Be can only be used as a tracer for Southern Ocean particle fluxes in the past if ocean circulation patterns and water mass residence times did not change significantly. ß

Section: Introductionmentioning

confidence: 59%

Section: Use Of 10 Be As Quasi-conservative Water Mass Tracer In the mentioning

confidence: 84%

Quasi-conservative behaviour of 10Be in deep waters of the Weddell Sea and the Atlantic sector of the Antarctic Circumpolar Current

Earth and Planetary Science Letters

Kubik

Mangini

2002

Self Cite

“…Atlantic sector of the ACC in the range 1.12-1.42 (Walter et al, 2000). The calculated burial 231 Pa/ 230 Th 389 activity ratio is 0.11 (Fig.6), well in excess of the production ratio of 0.093.…”

Section: Mass Balance Of Weddell Gyre 300mentioning

confidence: 88%

Meridional circulation across the Antarctic Circumpolar Current serves as a double 231Pa and 230Th trap

Earth and Planetary Science Letters

Venchiarutti

Stimac

et al. 2016

“…This may be due to some dissolution in the bottles, or to an error in the 230 Th -based correction for undertrapping. As the area where the traps were deployed is influenced by outflow of Weddell Sea water, the export of 230 Th from the Weddell Sea gives rise to a flux of 230 Th in excess of its production in the water column, thus biasing the normalization method (Walter et al, 2000a). The actual trapping efficiency would then be even lower, suggesting an influence of currents in the Frontal Jet down to depths over 1000m where trap collection efficiency is usually better (Scholten et al, 1999 ;Yu et al, 2000).…”

Section: 52sediment Trapsmentioning

confidence: 99%

“…This 230 Th calibration and exclusive use of core-top data reduces the estimates for present accumulation rates from the area of the Polar Front (46-53°S, n=5) by a factor of three to only 20-35 mmol m -2 yr -1 , a mere 1-2% of primary production ( Table 2). As a result of the export of 230 Th from the Weddell Sea mentioned above (Walter et al, 2000a), this correction may be somewhat too large, but it is clear that opal accumulation rates have previously been overestimated. It is likely that the lateral supply of sediment is also responsible for part of the diffusive fluxes measured at the sediment-water interface.…”

Section: Near the Polar Front In The Indianmentioning

confidence: 99%

Comparison of carbon and opal export rates between summer and spring bloom periods in the region of the Antarctic Polar Front, SE Atlantic

Deep Sea Research Part II: Topical Studies in Oceanography

Buesseler

Bathmann

et al. 2002

Although primary production in the Antarctic Circumpolar Current is not above the world average and carbon burial rates are low, 70% of the world's opal burial occurs in this zone and it has been suggested that blooms of large diatoms are responsible for this extraordinary situation. Here we compare export fluxes during bloom and steadystate situations near the Antarctic Polar Front in the SE Atlantic.In a previous expedition during the austral spring, we observed the development of a bloom that led to the sudden export of particles (Rutgers van der Loeff et al., 1997).Here we report the results of a second expedition to the same area in summer (DecJan), 3 years later. 234 Th was monitored in the surface water and in Rosette casts down to a water depth of 500m as tracer of export production in an intensive sampling program within a box of 275 x 375 km. Thus, whereas in spring we had observed a sudden increase from a negligible to a high export rate, the summer situation around the Polar Front was characterized by a lower but steady export rate. This summer flux contributes a similar fraction to the annual export budget as the previously observed spring bloom, which has higher export rates but a much shorter duration.