Nitrogen isotope constraints on subantarctic biogeochemistry

DiFiore, Peter J.; Sigman, Daniel M.; Trull, Thomas W.; Lourey, Martin; Karsh, Kristen; Cane, Greg; Ho, Ruby

doi:10.1029/2005jc003216

Cited by 84 publications

(160 citation statements)

References 67 publications

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“…In the case of the Subantarctic, the greatest violation of the Rayleigh model is the summertime lateral nitrate supply from the Antarctic Polar Frontal Zone (20). However, this is unlikely to be significant at ODP Site 1090, which is within the northern half of the Subantarctic Zone.…”

Section: Nitrate Drawdown During Ice Agesmentioning

confidence: 97%

“…Under conditions of light limitation, culture and modern field studies suggest that the isotope effect of nitrate assimilation is higher than the typical range of 4-6‰ (20,28,55,56 show a DB-δ 15 N decrease during ice ages, whereas some such occurrence would be expected if frontal migration were the dominant control on DB-δ 15 N change (25).…”

Section: Isotope Effect Of Nitrate Assimilationmentioning

confidence: 99%

“…Site 1090 is to the North of the deep mixed layers associated with the more polar Subantarctic (Fig. S7) The Subantarctic surface mixed layer has long been recognized as having multiple sources of water and nitrate on an annual basis (20,36,58,59). In the winter, deep mixing taps thermocline nitrate, which is the dominant source of nitrate consumed over the summer (20).…”

Section: Isotope Effect Of Nitrate Assimilationmentioning

confidence: 99%

“…These empirical points indicate that an increased degree of nitrate consumption in the Antarctic during the ice ages does not invalidate our interpretation of iron fertilization in the Subantarctic. The Subantarctic surface mixed layer has long been recognized as having multiple sources of water and nitrate on an annual basis (20,36,58,59). In the winter, deep of the resident nitrate by the end of the summer, the rest remaining from the prior winter/spring.…”

Section: Potential Impact Of Changing Antarctic Nitrate Consumption Onmentioning

confidence: 99%

“…In the Southern Ocean, where there is strong seasonal segregation of nitrate supply and nitrate consumption, the Rayleigh model provides a simple approximation for the N isotope systematics of summertime nitrate drawdown (53). According the Rayleigh model, the integrated phytoplankton biomass N produced from nitrate over the summer is expressed by the approximate "integrated product" equation: S7) (20,28). As the isotope effect increases, the δ 15 N of biomass produced tends to decrease, although there is convergence toward the δ 15 N of the nitrate supply as consumption approaches completion (Fig.…”

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confidence: 99%

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Iron Fertilization of the Subantarctic Ocean During the Last Ice Age

Martínez‐García

Sigman

Ren

et al. 2014

Science

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The sediment core TN057-06-PC4 (hereafter TN057-6) was retrieved from the Agulhas Ridge (42º 54.8' S, 8º 54.0' E, 3751 m) during the pre-site survey of the Ocean Drilling Program (ODP) Leg 177 at nearly the same position as ODP Site 1090 (42° 54.5′ S, 8° 54.0′ E, at 3,702 m). The high-resolution XRF Fe concentration records from ODP Site 1090 and TN57-06 were used to align the two cores using the software Analyseries (46). The good correlation of the two records after the alignment allows us to directly compare the measurements performed in the two cores with minimal stratigraphic uncertainty (Fig. S1a). This indicates that the 230 Th measurements performed in can be used to reconstruct sedimentary fluxes of different elements and/or organic compounds in both records.For example, in Figure S1c, the high-resolution 230 Th-normalized mass flux (Fig.S1b) was used to calculate iron fluxes both in ODP Site 1090 and TN057-6 ( The age model of our record was generated by graphic correlation of the highresolution 230 Th-normalized Fe flux from ODP Site 1090 to the most recent ice core dust reconstruction from EPICA Dome C (44), using ice core chronology (AICC2012) (47,48) (Fig. S2). This new age model is generally in good agreement with the original ages proposed by Venz and Hodell 2002 (65) using benthic δ 18 O stratigraphy (Fig. S3). The good correlation of ODP Site 1090 Fe flux and EDC dust records down to sub-millennial timescales allows us to directly compare our marine data to other ice core measurements (e.g., atmsopheric pCO 2 ) with minimal stratigraphic uncertainty (Fig. S2). Foraminifera-bound δ 15 N analysisAround 600-800 specimens of G. bulloides and O. universa were picked manually under a dissecting microscope (250-425--6 mg of clean foraminiferal calcite. Foraminifera-bound δ 15 N was measured at Princeton University following the protocol described in (23,32). In the intervals where foraminifera abundances were adequate, samples were measured in duplicate. The reported error 2 bars in Fig. S9 represent the standard deviation estimated from the means of duplicated measurements. The average standard deviation of all the replicated measurements (from foraminifera-bound organic matter oxidation onward) was 0.19‰. Bulk sediment δ 15 N and %Nitrogen analysisThe N content and δ 15 N of the bulk sediment were analyzed using a Thermo FisherSeries 1112 elemental analyzer coupled with a Thermo Fisher Delta V Plus mass spectrometer at ETH Zurich. Between 50 and 100 mg of sediment were used for eachanalysis. An in-house peptone standard, which has been referenced to international reference materials (IAEA-N1 and IAEA-N2), was measured in each sample run and used for the final corrections. The standard deviation for the peptone standard among the different runs was <0.1‰. 230 Th and opal analysisConcentrations of U and Th isotopes were measured by inductively coupled-plasma mass spectrometry after strong acid sediment digestion and chromatographic separation as described by Fleisher and Anderson, 2003 (49). Opal...

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Section: Nitrate Drawdown During Ice Agesmentioning

confidence: 97%

Section: Isotope Effect Of Nitrate Assimilationmentioning

confidence: 99%

Section: Isotope Effect Of Nitrate Assimilationmentioning

confidence: 99%

Section: Potential Impact Of Changing Antarctic Nitrate Consumption Onmentioning

confidence: 99%

mentioning

confidence: 99%

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Iron Fertilization of the Subantarctic Ocean During the Last Ice Age

Martínez‐García

Sigman

Ren

et al. 2014

Science

Self Cite

412

433

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The counterintuitive effect of summer‐to‐fall mixed layer deepening on eukaryotic new production in the Sargasso Sea

Fawcett

Lomas

Ward

et al. 2014

Global Biogeochemical Cycles

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The Sargasso Sea is characterized by strong summertime stratification that is thought to drive oligotrophy, but export production is surprisingly similar to that of high-latitude regions with ample major nutrient supply. Here we use the summer-to-fall progression in the northwestern Sargasso Sea to investigate the relationship between upper ocean stratification and phytoplankton nitrogen (N) uptake. Euphotic zone particles collected in July, October, and December were sorted by flow cytometry, and the 15 N/ 14 N of separated prokaryotic and eukaryotic phytoplankton was analyzed. The 15 N/ 14 N of Prochlorococcus and Synechococcus was always low, indicating uniform reliance on recycled N. In July and in two fall profiles, the 15 N/ 14 N of eukaryotic phytoplankton was high, reflecting consumption of subsurface nitrate. In three other fall profiles, eukaryotic 15 N/ 14 N was similar to prokaryote 15 N/ 14 N, suggesting a shift toward more complete reliance on recycled N. The progressive deepening of the mixed layer from summer to fall, although reducing the surface-to-deep density contrast, increases the density difference of the euphotic zone as a whole from underlying nutrient-rich waters, which may play a role in the observed decline in euphotic zone nitrate supply into the fall. The apparent summertime nitrate supply to the euphotic zone, when the mixed layer is shallowest, may help to explain the surprisingly high export production of the subtropical and tropical ocean.

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Hourly oxygen and total gas tension measurements at the Southern Ocean Time Series site reveal winter ventilation and spring net community production

Weeding

Trull

2014

JGR Oceans

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[1] Using a moored instrument package at 35 m depth at the Southern Ocean Time Series (SOTS) site near 46 56 0 S 142 15 0 E from September 2010 to April 2011 (219 days), we obtained the first Southern Ocean Time Series of dissolved oxygen (from an optode sensor) and nitrogen (from a total gas tension sensor). Nitrogen was consistently supersaturated (100.8%-102.9%), while oxygen was highly subsaturated in early spring (as low as 93.5%) and reached supersaturation (maximum 104.9%) during only 37 days in early summer. The low oxygen levels in spring illustrate the importance of deep mixing in the Subantarctic Zone in ventilating the upper limb of the global overturning circulation. Using nitrogen as a proxy for physical processes, we isolated biological contributions to the oxygen time series to obtain net community production (NCP). Almost all NCP occurred in spring in the presence of deep mixed layers, with only small additional contributions in summer after water column stratification. The temperature and salinity time series also revealed distinct parcels of water. Rapid changes at their interfaces generated unrealistic NCP events in the standard calculation model, which were removed, while still retaining NCP contributions from each parcel. NCP totaled 2.2 6 1.2 mol O 2 m 22 over the deployment, within the range of previous estimates from low temporal resolution techniques. Examination of errors revealed particular sensitivity to entrainment, suggesting more rigorous understanding of this process is required, e.g., via profiling instruments.Citation: Weeding, B., and T. W. Trull (2014), Hourly oxygen and total gas tension measurements at the Southern Ocean Time Series site reveal winter ventilation and spring net community production,

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Nitrogen isotope constraints on subantarctic biogeochemistry

Cited by 84 publications

References 67 publications

Iron Fertilization of the Subantarctic Ocean During the Last Ice Age

Iron Fertilization of the Subantarctic Ocean During the Last Ice Age

The counterintuitive effect of summer‐to‐fall mixed layer deepening on eukaryotic new production in the Sargasso Sea

Hourly oxygen and total gas tension measurements at the Southern Ocean Time Series site reveal winter ventilation and spring net community production

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