Radium isotopes as tracers of iron sources fueling a Southern Ocean phytoplankton bloom

Charette, Matthew A.; Gonneea, M. E.; Morris, Paul J.; Statham, Peter J.; Fones, Gary R.; Planquette, Hélène; Salter, Ian; Garabato, Alberto C. Naveira

doi:10.1016/j.dsr2.2007.06.003

Cited by 95 publications

(111 citation statements)

References 29 publications

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“…In this case, K z can be calculated from slope (s) of a plot of ln ( 228 Ra/ 226 Ra) vs. depth (K z = λ/s 2 ). The model assumes a constant, steadystate source of 228 Ra in the surface mixed layer and does not take into account lateral input of 228 Ra below the surface mixed layer (Charette et al, 2007). We applied this tracer-based model of vertical exchange to 228 Ra/ 226 Ra data from station 21 (Fig.…”

Section: Discussionmentioning

confidence: 99%

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Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

et al. 2013

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Radium has four naturally occurring isotopes that have proven useful in constraining water mass source, age, and mixing rates in the coastal and open ocean. In this study, we used radium isotopes to determine the fate and flux of runoff-derived cesium from the Fukushima Dai-ichi Nuclear Power Plant (FNPP). During a June 2011 cruise, the highest cesium (Cs) concentrations were found along the eastern shelf of northern Japan, from Fukushima south, to the edge of the Kuroshio Current, and in an eddy ~ 130 km from the FNPP site. Locations with the highest cesium also had some of the highest radium activities, suggesting much of the direct ocean discharges of Cs remained in the coastal zone 2–3 months after the accident. We used a short-lived Ra isotope (²²³Ra, t_1/2 = 11.4 d) to derive an average water mass age (T_r) in the coastal zone of 32 days. To ground-truth the Ra age model, we conducted a direct, station-by-station comparison of water mass ages with a numerical oceanographic model and found them to be in excellent agreement (model avg. T_r = 27 days). From these independent T_r values and the inventory of Cs within the water column at the time of our cruise, we were able to calculate an offshore ¹³⁴Cs flux of 3.9–4.6 × 10¹³ Bq d⁻¹. Radium-228 (t_1/2 = 5.75 yr) was used to derive a vertical eddy diffusivity (K_z) of 0.7 m² d⁻¹ (0.1 cm² s⁻¹); from this K_z and ¹³⁴Cs inventory, we estimated a ¹³⁴Cs flux across the pycnocline of 1.8 × 10⁴ Bq d⁻¹ for the same time period. On average, our results show that horizontal mixing loss of Cs from the coastal zone was ~ 10⁹ greater than vertical exchange below the surface mixed layer. Finally, a mixing/dilution model that utilized our Ra-based and oceanographic model water mass ages produced a direct ocean discharge of ¹³⁴Cs from the FNPP of 11–16 PBq at the time of the peak release in early April 2011. Our results can be used to calculate discharge of other water-soluble radionuclides that were released to the ocean directly from the Fukushima NPP

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Section: Discussionmentioning

confidence: 99%

“…Moore, 2000;Dulaiova et al, 2009) and land-ocean fluxes of dissolved trace elements and isotopes (e.g. Krest et al, 2000;Charette et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

et al. 2013

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“…Using a 600 km shoreline and a bloom area of 90 000 km 2 (Charette et al, 2007), the cumulative effect of this horizontal flux is estimated to be up to 390 nmol m -2 d -1 which is considerably higher than either the atmospheric or vertical inputs (Figure 9). …”

Section: Lateral Sources Of Fe From the Island Systemmentioning

confidence: 99%

Dissolved iron in the vicinity of the Crozet Islands, Southern Ocean

Planquette

Statham

Fones

et al. 2007

Deep Sea Research Part II: Topical Studies in Oceanography

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The annual phytoplankton bloom occurring north of the Crozet Plateau provides a rare opportunity to examine the hypothesis that natural iron fertilisation can alleviate HNLC conditions normally associated with the Southern Ocean. Therefore, during CROZEX, a large multidisciplinary study performed between November 2004 and January 2005, measurements of total dissolved iron (DFe, 0.2 m) were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples. waters. Enrichment of dissolved iron (>1 nM) at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron. Waters further north also appear to be affected by this input of coastal and shelf origin, although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of ~ 0.07 nM.km -1 at the time of sampling. Using lateral and vertical diffusion coefficients derived from Ra isotope profiles and also estimates of atmospheric inputs, it was then possible to estimate a DFe concentration of ~ 0.55 nM to the north of the islands prior to the bloom event, which is sufficient to initiate the bloom, the lateral island source being the largest component. A similar situation is observed for other Sub-Antarctic Islands such as Kerguelen, South Georgia, that supply dissolved iron to their surrounding waters, thus, enhancing chlorophyll concentrations.Keywords: Dissolved Iron, Crozet Islands, Southern Ocean, HNLC. Planquette et al., 26/04/07 3 The hypothesis that iron can act as a limiting micro nutrient in High Nutrient Low Chlorophyll (HNLC hereafter) regions is now generally accepted and has been investigated on a number of occasions (Boyd et al., 2000;de Baar et al., 2005). IntroductionThe iron hypothesis originally proposed by Martin (1990) has led to numerous studies which all demonstrate that the addition of iron to HNLC waters causes an increase in phytoplankton productivity. Subsequent investigations into iron's role in phytoplankton physiology have also revealed important findings. Among them, one can cite its role in photosynthetic and respiratory electron transport, nitrate reduction, and chlorophyll synthesis (Sunda and Huntsman, 1995; Sunda and Huntsman, 1997). The broader implication is that in HNLC waters, the presence of iron can increase the efficiency of the biological pump and promote drawdown of atmospheric carbon dioxide (Bakker et al., 2001;Bakker et al., 2005; Boyd et al., 2004; Law et al., 2006;Martin et al., 1990).The Southern Ocean is subjected to these HNLC conditions and is depicted as the largest potential sink of anthropogenic CO 2 in the global ocean (Martin, 1990; Tréguer and Pondaven, 2001) and as a key system in the context of climate change (Sarmiento et al., 1998). However, due to the existence of distinct regional sub systems differing in their physical and biological properties (Arrigo et al., 1998; Tréguer and Jacques, 1992), this ocean should not be viewed as one entity.Ther...

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“…The KEOPS-2 cruise was conducted during austral spring 2011 to the east of the Kerguelen Islands. Natural radio-tracers such as radium isotopes ( 223 Ra, T 1/2 = 11.4 d; 224 Ra, T 1/2 = 3.66 d; 228 Ra, T 1/2 = 5.75 yr) have already been proved to be powerful tools to track the origin and fate of chemical elements -including iron and other micronutrients -which are released by the sediments deposited on the shelves (Annett et al, 2013;van Beek et al, 2008;Charette et al, 2007;Dulaiova et al, 2009;Sanial et al, 2014). In this work, we refer to these latter inputs as "sediment-derived inputs".…”

Section: Sanial Et Al: Use Of Ra Isotopes To Deduce Rapid Transfementioning

confidence: 99%

Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

et al. 2015

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Abstract. The Southern Ocean is known to be the largest high-nutrient, low-chlorophyll (HNLC) region of the global ocean due to iron limitation. However, a large phytoplankton bloom develops annually downstream of the Kerguelen Islands, a bloom which is sustained partly by iron released from the sediments deposited onto the shelves. In the framework of the KEOPS-2 project, we used radium isotopes ( 224 Ra, T 1/2 = 3.66 d; 223 Ra, T 1/2 = 11.4 d; 228 Ra, T 1/2 = 5.75 yr) to provide information on the origin of iron fertilization and on the timescales of the transfer of sedimentderived inputs (including iron and other micronutrients) towards offshore waters. Significant 224 Ra and 223 Ra activities were found in the near vicinity of the Kerguelen Islands, in agreement with the short half-lives of these isotopes. Significant 224 Ra and 223 Ra activities were also detected up to 200 km downstream of the islands and more unexpectedly in offshore waters south of the polar front. These observations thus clearly indicate (i) that the sediment-derived inputs are rapidly transferred towards offshore waters (on timescales on the order of several days up to several weeks) and (ii) that the polar front is not a physical barrier for the chemical elements released from the sediments of the Kerguelen Plateau. The Ra data set suggests that iron and other micronutrients released by the shelves of the Kerguelen Islands may contribute to fueling the phytoplankton bloom downstream of the islands, despite the presence of the polar front. However, the heterogeneous distribution of the 224 Ra and 223 Ra activities in surface waters suggests that this supply across the front is not a continuous process but rather a process that is highly variable in space and time.

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Radium isotopes as tracers of iron sources fueling a Southern Ocean phytoplankton bloom

Cited by 95 publications

References 29 publications

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

Radium-based estimates of cesium isotope transport and total direct ocean discharges from the Fukushima Nuclear Power Plant accident

Dissolved iron in the vicinity of the Crozet Islands, Southern Ocean

Use of Ra isotopes to deduce rapid transfer of sediment-derived inputs off Kerguelen

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