Iron Fertilization of the Subantarctic Ocean During the Last Ice Age

Abstract

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...

Planktic foraminifer and coccolith contribution to carbonate export fluxes over the central Kerguelen Plateau

“…The higher efficiency of the biological pump was likely linked to higher deposition of eolian iron and more complete utilization of nutrients at high latitudes (Mahowald et al, 2006;Martínez-García et al, 2014). Our results from naturally fertilized Southern Ocean blooms suggest that the magnitude of the associated carbonate counter pump (Salter et al, 2014) depends not only on the dominant calcifying planktonic organisms (foraminifers versus coccolithophores), but also on the species assemblage that responds to the increase in primary production.…”

Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion

“…The result was a pronounced, synchronous, ∼50% decline in SH dust deposition (Fig. 1), reducing ocean biological uptake (10,46) and thereby sharply reducing the ocean CO 2 sink. In Patagonia and New Zealand, warmer and dryer conditions south of ∼35°S (37) led to the well-documented retreat of glaciers (4-6) that starved glacial outwash plains of their fine-sediment resupply (45), with lower wind speeds possibly also contributing to reduced dustiness (47).…”

“…Superimposed on this smooth, orbital-scale variability are abrupt changes in climate, resulting in substantial variations among glacial terminations (2) and suggesting that the evolution of each deglaciation may be influenced by climate drivers specific to that deglaciation (3). One such rapid change during the last termination began ∼17.7 ky before 1950 (17.7 ka), when paleoclimate records show sharp, nearly synchronous changes across the Southern Hemisphere (SH) such as a widespread retreat of glaciers in Patagonia (4,5) and New Zealand (6), onset of rapid lake expansion in the Bolivian Andes (7), increases in summertime precipitation in subtropical Brazil (8), decreases in southern Australian aridity (9), and dust deposition recorded in ocean sediment cores (9,10) (Fig. 1).…”

Diagnosing oceanic nutrient deficiency

“…Hence strong upwelling acts to maintain Fe deficiency ( figure 3b) (figure 3a) in the surface SO [7]. Past alterations in the nutrient status and BCP efficiency of the SO thus need to be considered in the context of the strength of Fe deficient sub-surface nutrient resupply, alongside the potential for enhanced non-internal Fe sources from dust [15].…”

“…Establishing where, when and how certain nutrients come to be limiting in the upper ocean represents a key challenge for our understanding of the Earth system [11,13] alongside the behaviour of this system over a range of timescales [14,15]. The extent of this challenge is only emphasized through ongoing recognition that, alongside the so-called macronutrients (N, P and Si), the oceanic cycling of many of the trace metal elements (e.g.…”