A Method for Quantifying Deep-Sea Carbonate Dissolution Using14C Dating (original) (raw)
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Late Pleistocene evolution of the ocean's carbonate system
We demonstrate that the carbonate record from a single site (Ocean Drilling Program Site 1089) in the deep South Atlantic represents a qualitative, high-resolution record of the temporal evolution of the carbonate saturation state of the deep sea. The record is especially notable because it is free from many of the complications that limit other records (low sedimentation rates, blurring by chemical erosion, bioturbation, etc.). The pattern of carbonate variability is characteristic of Indo-Pacific cores with high-carbonate glacials and low-carbonate interglacials. Wt% carbonate lags changes in benthic δ18O by an average of ~7.6 kyr, and carbonate variations are in-phase with the rate of change (first derivative) of benthic δ18O. Intense dissolution occurs at the transition from interglacial to glacial periods and increased preservation occurs during deglaciations. These observations represents two fundamentally different responses of the marine carbonate system. The lagged response of carbonate to δ18O reflects a steady-state mass balance process whereby the lysocline adjusts to maintain alkalinity balance between riverine input and marine burial. The Site 1089 carbonate signal is remarkably similar to inferred changes in the Sr/Ca of seawater for the past 250 kyr, which implies that both carbonate dissolution and seawater Sr/Ca may be controlled by sea level-induced changes in the location of carbonate deposition (shelf-basin fractionation) during glacial to interglacial cycles. The transient change in preservation during the transitions into and out of glacial stages reflects a response of the carbonate system to a redistribution of alkalinity and DIC in the ocean (i.e. carbonate compensation). Comparison of the Site 1089 carbonate and Vostok pCO2 records suggests a role of deep-sea [CO2 3 -] variations for governing at least some second-order features of the atmospheric pCO2 signal. In order to quantify this role, however, measurement of indices of dissolution along a true depth transect will be required to estimate the magnitudes of changes in deep-sea [CO2 3 -]. © 2001 Elsevier Science B.V. All rights reserved.
In situ measurements of calcium carbonate dissolution rates in deep-sea sediments
Geochimica et Cosmochimica Acta, 1990
Benthic fluxes of alkalinity, carbon dioxide, and oxygen have been measured using an in situ incubation chamber at three sites (MANOP Sites C and S and PACFLUX Site SC) in the central equatorial north Pacific. At two carbonate-rich sites (C and SC), a budget for oxygen, alkalinity, and TCOz fluxes indicate a net CaCOs dissolution rate of approximately 0.4 mmol m-' day-'. This rate is only 20% of previous estimates but is consistent with a dissolution rate constant predicted from laboratory experiments with deepsea sediments and derived from in situ flux measurements in sediments of the southern California borderland. Organic matter oxidation in the sediment column provides the acid for 60-100% of the calcium carbonate dissolution occurring at these sites with the remainder derived from undersaturated bottom water. At a low-carbonate site (S), no carbonate dissolution in the sediment or on the sea floor is apparent, although sediment traps indicate a rain of CaC03 through 3400 m. The rates of remineralization relative to resuspension or erosion at this site must differ for organic carbon and calcium carbonate, so that carbonate grains reaching the sea floor are physically removed by erosion or resuspension before they dissolve, while organic carbon is largely oxidized before it can be physically removed.
Quaternary Science Reviews, 2013
26 27 28 29 30 Submit to Quaternary Science Reviews as an Article 31 32 33 34 Highlights: 35 New [CO 3 2-] for the intermediate Atlantic and deep Pacific during 0-160 ka; 36 37 [CO 3 2-] records show both temporal and transient changes that differ from 13 C; 38 39 The MIS 5c-to-3 [CO 3 2-] rise is consistent with the "coral-reef" hypothesis; 40 41 Vertical carbon shifting affects [CO 3 2-] variations at MIS 4 and 2; 42 43 Deep water [CO 3 2-] controlled CaCO 3 preservation in the deep Pacific. 44 45 46 Abstract 47 We present new deep water carbonate ion concentration ([CO 3 2-]) records, reconstructed 48 using Cibicidoides wuellerstorfi B/Ca, for one core from Caribbean Basin (water depth = 3623 49 m, sill depth = 1.8 km) and three cores located at 2.3-4.3 km water depth from the equatorial 50 Pacific Ocean during the last glacial-interglacial cycle. The pattern of deep water [CO 3 2-] in the 51 Caribbean Basin roughly mirrors that of atmospheric CO 2 , reflecting a dominant influence from 52 preformed [CO 3 2-] in the North Atlantic Ocean. Compared to the amplitude of ~65 mol/kg in 53 the deep Caribbean Basin, deep water [CO 3 2-] in the equatorial Pacific Ocean has varied by no 54 more than ~15 mol/kg due to effective buffering of CaCO 3 on deep-sea pH in the Pacific 55 Ocean. Our results suggest little change in the global mean deep ocean [CO 3 2-] between the Last 56 Glacial Maximum (LGM) and the Late Holocene. The three records from the Pacific Ocean 57 show long-term increases in [CO 3 2-] by ~7 mol/kg from Marine Isotope Stage (MIS) 5c to mid 58 MIS 3, consistent with the response of the deep ocean carbonate system to a decline in neritic 59 carbonate production associated with ~60 m drop in sea-level (the "coral-reef" hypothesis). 60 Superimposed upon the long-term trend, deep water [CO 3 2-] in the Pacific Ocean displays 61 transient changes, which decouple with 13 C in the same cores, at the start and end of MIS 4. 62 These changes in [CO 3 2-] and 13 C are consistent with what would be expected from vertical 63 nutrient fractionation and carbonate compensation. The observed ~4 mol/kg [CO 3 2-] decline in 64 the two Pacific cores at >3.4 km water depth from MIS 3 to the LGM indicate further 65 strengthening of deep ocean stratification, which contributed to the final step of atmospheric CO 2 66 drawdown during the last glaciation. The striking similarity between deep water [CO 3 2-] and 67 230 Th-normalized CaCO 3 flux at two adjacent sites from the central equatorial Pacific Ocean 68 provides convincing evidence that deep-sea carbonate dissolution dominantly controlled CaCO 3 69 3 preservation at these sites in the past. Our results offer new and quantitative constraints from 70 deep ocean carbonate chemistry to understand roles of various mechanisms in atmospheric CO 2 71 changes over the last glacial-interglacial cycle. 72 73 Keywords: deep ocean carbonate ion, global carbon cycle, B/Ca, carbonate compensation, ocean 74 stratification, Pleistocene 75 76 77
Paleoceanography, 1996
In order to investigate the paleoceanographic record of dissolution of calcium carbonate (CaCO3) in the central equatorial Pacific Ocean, we have studied the relationship between three indices of foraminiferal dissolution and the concentration and accumulation of CaCO3, opal, and Corg in Core WEC8803B-GC51 (1.3øN, 133.6øW; 4410 m). This core spans the past 413 kyr of deposition and moved in and out of the lysoclinal transition zone during glacial-interglacial cycles of CaCO3 production and dissolution. The record of dissolution intensity provided by foraminiferal fragmentation, the proportion of benthic foraminifera, and the foraminiferal dissolution index consistently indicates that the past corrosion of pelagic CaCO3 in the central equatorial Pacific does not vary with the observed sedimentary concentration of CaCO3. Although there is a weak low-frequency variation (~100 kyr) in dissolution intensity, it is unrelated to sedimentary CaCO3 concentration. There are many shorter-lived episodes where high CaCO3 concentration is coincident with poor foraminiferal preservation, and where, conversely, low CaCO3 concentration is coincident with superb foraminiferal preservation. Spectral analyses indicate that dissolution maxima consistently lagged glacial maxima (manifest by the SPECMAP •180 stack) in the 100-kyr orbital band. Additionally, there is no relationship between dissolution and the accumulation of biogenic opal or Corg or between dissolution and the burial ratio of Corg / CINorg (calculated from Corg and CaCO3). Because previous studies of this core strongly suggest that surface water productivity varied closely with CaCO3 accumulation, both the mechanistic decoupling of carbonate dissolution from CaCO3 concentration (and from biogenic accumulation) and the substantial phase shift between dissolution and global glacial periodicity effectively obscure any simple link between export production, CaCO3 concentration, and dissolution of sedimentary CaCO3.
Evidence for a reduction in the carbonate ion content of the deep sea during the course of the …
Paleoceanography
The palco carbonate ion proxy proposed by Broecker et al. [1999] is applied in a search for trends in the Holocene acidity of waters in the transition zone between North Atlantic Deep Water and Antarctic Bottom Water (AABW). A clear signal emerges that the carbonate ion content of waters in this zone declined during the past 8000 years. In order to determine whether this decline represents a strengthening of the northward penetrating tongue of low co• content AABW or a global reduction of co• ion, measurements were made on a core from the Ontong Java Plateau in the western equatorial Pacific. Evidence for a similar decline in co• ion over the course of the Holocene was obtained lending support of the latter explanation. Such a drop is consistent with the recent finding by Indermfihle et al. [1999] that the CO2 content of the atmosphere (as recorded in the Taylor Dome Antarctica ice core) rose by 20-25 ppm during the past 8000 years.
Paleoceanography, 2009
1] Eocene Thermal Maximum 2 (ETM2 or H1; 53.7Ma)representsashort−livedwarmingepisode,associatedwiththeinjectionofalargemassof13C−depletedcarbonintotheocean−atmospheresystem.Themassofinjectedcarbon,theextentofdeepseadissolution,andtheamountofwarmingduringETM2appeartobeapproximatelyhalfofthosedocumentedforthePaleocene−Eocenethermalmaximum(PETM,53.7 Ma) represents a short-lived warming episode, associated with the injection of a large mass of 13 C-depleted carbon into the ocean-atmosphere system. The mass of injected carbon, the extent of deep sea dissolution, and the amount of warming during ETM2 appear to be approximately half of those documented for the Paleocene-Eocene thermal maximum (PETM, 53.7Ma)representsashort−livedwarmingepisode,associatedwiththeinjectionofalargemassof13C−depletedcarbonintotheocean−atmospheresystem.Themassofinjectedcarbon,theextentofdeepseadissolution,andtheamountofwarmingduringETM2appeartobeapproximatelyhalfofthosedocumentedforthePaleocene−Eocenethermalmaximum(PETM,55.5 Ma), but the pattern of lysocline migration during ETM2 has not yet been documented sufficiently to decipher potential differences in carbon sources and sequestration mechanisms. We present high-resolution carbonate dissolution and bulk stable isotope records across ETM2 and the successive H2 event ($53.6 Ma) on a common age model for four sites along the Walvis Ridge depth transect (1500 to 3600 m paleowater depth) to assess lysocline evolution. The onset of ETM2 is characterized by multiple, depth-dependent transitions of carbonate dissolution (up to 9696% of the total flux), associated with rapid depletions in bulk carbonate carbon (up to 961-1.5%) and oxygen (up to 0.7−1.50.7-1.5%) isotope values. H2 shows a 0.7−1.50.7% negative carbon isotope excursion, with a coeval decrease in d 18 O of 0.50.5% and 0.580% of carbonate dissolution. During ETM2, the lysocline recovered within $30 ka. We attribute this rapid recovery to terrestrial CaCO 3 neutralization through enhanced chemical weathering of carbonates in soils and rocks. According to theory, carbonate dissolution was lower after recovery than prior to ETM2, indicating carbonate ion oversaturation and a deeper position of the lysocline. Spectral analysis indicates that the changes in carbonate dissolution and d 13 C values were precession paced, implying that weathering feedbacks and short-term perturbations in the carbon cycle were important in determining early Eocene background and hyperthermal ocean [CO 3 2À ] conditions. Citation: Stap, L., A. Sluijs, E. Thomas, and L. Lourens (2009), Patterns and magnitude of deep sea carbonate dissolution during Eocene Thermal Maximum 2 and H2, Walvis Ridge, southeastern Atlantic Ocean, Paleoceanography, 24, PA1211,
Quaternary Science Reviews, 2006
The Mid-Brunhes dissolution interval (MBDI) represents a period of global carbonate dissolution, lasting several hundred thousand years, centred around Marine Isotope Stage (MIS) 11. Here we report the effects of dissolution in ODP core 982, taken from 1134 m in the North Atlantic. Paradoxically, records of atmospheric CO 2 from Antarctic ice-cores reveal no long term trend over the last 400 kyr and suggest that CO 2 during MIS 11 was no higher than during the present interglacial. We suggest that a global increase in pelagic carbonate production during this period, possibly related to the proliferation of the Gephyrocapsa coccolithophore, could have altered marine carbonate chemistry in such a way as to drive increased dissolution under the constraints of steady state. An increase in the production of carbonate in surface waters would cause a drawdown of global carbonate saturation and increase dissolution at the seafloor. In order to reconcile the record of atmospheric CO 2 variability we suggest that an increase in the flux of organic matter from the surface to deep ocean, associated with either a net increase in primary production or the enhanced ballasting effect provided by an increased flux of CaCO 3 , could have countered the effect of increased calcification on CO 2 .
Global deep-sea burial rate of calcium carbonate during the last glacial maximum
Paleoceanography, 13, 298-310, 1998
Global databases of calcium carbonate concentrations and mass accumulation rates in Holocene and last glacial maximum sediments were used to estimate the deep-sea sedimentary calcium carbonate burial rate during these two time intervals. Sparse calcite mass accumulation rate data were extrapolated across regions of varying calcium carbonate concentration using a gridded map of calcium carbonate concentrations and the assumption that accumulation of noncarbonate material is uncorrelated with calcite concentration within some geographical region. Mean noncarbonate accumulation rates were estimated within each of nine regions, determined by the distribution and nature of the accumulation rate data. For core-top sediments the regions of reasonable data coverage encompass 67% of the high-calcite (>75%) sediments globally, and within these regions we estimate an accumulation rate of 55.9 ± 3.6×1011 mol yr−1. The same regions cover 48% of glacial high-CaCO3 sediments (the smaller fraction is due to a shift of calcite deposition to the poorly sampled South Pacific) and total 44.1 ± 6.0×1011 mol yr−1. Projecting both estimates to 100 % coverage yields accumulation estimates of 8.3×1012 mol yr−1 today and 9.2×1012 mol yr−1 during glacial time. This is little better than a guess given the incomplete data coverage, but it suggests that glacial deep sea calcite burial rate was probably not considerably faster than today in spite of a presumed decrease in shallow water burial during glacial time.
Neritic and pelagic carbonate sedimentation in the marine environment: ignorance is not bliss
Geologische Rundschau, 1996
Synthesis of available data allows us to define general patterns of late Quaternary carbonate production and sedimentation in the global ocean. During high stands of sea level, the neritic and pelagic environments appear to sequester approximately similar amounts of carbonate, whereas during low stands of sea level the decreased neritic zone produces and accumulates approximately an order of magnitude less carbonate. Assuming that global accumulation of deep-sea carbonates remains more or less constant during glacially induced changes in sea level, the ocean becomes depleted with respect to calcium carbonate during high stands and recharges during low stands. Before we can achieve a better understanding of the global carbonate system, however, we need a better understanding of key environments and processes: (a) production and accumulation on continental shelves both as potential sinks (accumulation) and as sources (export to the deep sea); (b) a better measure of pelagic carbonate production; and (c) late Quaternary (late Pleistocene and Holocene) mass accumulation rates in the deep sea.