NAO signature in a Bermuda coral Sr/Ca record

Kuhnert, Henning; Crüger, Traute; Pätzold, Jürgen

doi:10.1029/2004gc000786

Cited by 40 publications

(34 citation statements)

References 46 publications

(64 reference statements)

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“…5). Additional evidence in support of this hypothesis is provided by coral cores from Bermuda that exhibit thicker layers of CaCO 3 deposition, and therefore greater rates of calcification, corresponding to years of negative SST anomalies (indicative of deeper MLD) (31,32), negative winter NAO events (33), and presumably higher offshore productivity (25,26).…”

Section: Resultsmentioning

confidence: 92%

Shifts in coral reef biogeochemistry and resulting acidification linked to offshore productivity

Yeakel

Andersson

Bates

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Oceanic uptake of anthropogenic carbon dioxide (CO 2 ) has acidified open-ocean surface waters by 0.1 pH units since preindustrial times. Despite unequivocal evidence of ocean acidification (OA) via open-ocean measurements for the past several decades, it has yet to be documented in near-shore and coral reef environments. A lack of long-term measurements from these environments restricts our understanding of the natural variability and controls of seawater CO 2 -carbonate chemistry and biogeochemistry, which is essential to make accurate predictions on the effects of future OA on coral reefs. Here, in a 5-y study of the Bermuda coral reef, we show evidence that variations in reef biogeochemical processes drive interannual changes in seawater pH and Ω aragonite that are partly controlled by offshore processes. Rapid acidification events driven by shifts toward increasing net calcification and net heterotrophy were observed during the summers of 2010 and 2011, with the frequency and extent of such events corresponding to increased offshore productivity. These events also coincided with a negative winter North Atlantic Oscillation (NAO) index, which historically has been associated with extensive offshore mixing and greater primary productivity at the Bermuda Atlantic Time-series Study (BATS) site. Our results reveal that coral reefs undergo natural interannual events of rapid acidification due to shifts in reef biogeochemical processes that may be linked to offshore productivity and ultimately controlled by larger-scale climatic and oceanographic processes.O cean acidification (OA) resulting from rising atmospheric CO 2 (1-3) and the associated declines in surface seawater pH and saturation state with respect to CaCO 3 minerals such as aragonite (Ω aragonite = [Ca 2+ ][CO 3 2-]/K sp *, where K sp * is the ion solubility product) have raised concerns on the potential consequences to marine calcifiers and ecosystems (4, 5). Reductions in Ω aragonite have been found to negatively affect organismal CaCO 3 production (6) while accelerating bioerosion and CaCO 3 dissolution (7,8). Hence, it has been hypothesized that coral reefs could shift from a condition of net calcification to net dissolution, with some model estimates predicting a transition for worldwide reefs at atmospheric CO 2 levels of 560 ppm (5, 7).Despite growing concern about the vulnerability of coral reefs, a lack of long-term measurements has prevented direct observation of anthropogenic OA owing to increasing atmospheric CO 2 in these environments. Additionally, short-term observations have revealed large variability and modification of reef seawater CO 2 -carbonate chemistry on diurnal and seasonal timescales as a result of coral reef biogeochemical processes such as photosynthesis, respiration, calcification, and CaCO 3 dissolution (9, 10). It has been hypothesized that these natural processes, quantified as net ecosystem production (NEP = gross primary production − autotrophic and heterotrophic respiration) and net ecosystem calcification (NEC = gro...

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Section: Resultsmentioning

confidence: 92%

Shifts in coral reef biogeochemistry and resulting acidification linked to offshore productivity

Yeakel

Andersson

Bates

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…1), than do corals from North Rock 17,18 . Differences between the north and south have been found in sea surface temperature (SST) records generated from coral Sr/Ca that are attributed to differences in coastal circulation 19 . Studies from the north reef have found agreement between seasonal variations in coral Sr/Ca and SST data from Hydrostation S; however, there is no relationship between North Rock Sr/Ca and SST at interannual timescales (that is, comparing data for wintertime only) 19,20 .…”

Section: Carbon Isotope Records From Bermudamentioning

confidence: 99%

“…Differences between the north and south have been found in sea surface temperature (SST) records generated from coral Sr/Ca that are attributed to differences in coastal circulation 19 . Studies from the north reef have found agreement between seasonal variations in coral Sr/Ca and SST data from Hydrostation S; however, there is no relationship between North Rock Sr/Ca and SST at interannual timescales (that is, comparing data for wintertime only) 19,20 . This indicates that the Sr/Ca to SST correlation is driven by the seasonal cycle that occurs each year in both records rather than the North Rock Sr/Ca accurately capturing interannual ocean conditions in the southern and central Sargasso Sea.…”

Section: Carbon Isotope Records From Bermudamentioning

confidence: 99%

Two centuries of limited variability in subtropical North Atlantic thermocline ventilation

et al. 2012

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Ventilation and mixing of oceanic gyres is important to ocean-atmosphere heat and gas transfer, and to mid-latitude nutrient supply. The rates of mode water formation are believed to impact climate and carbon exchange between the surface and mid-depth water over decadal periods. Here, a record of 14 C/ 12 C (1780-1940), which is a proxy for vertical ocean mixing, from an annually banded coral from Bermuda, shows limited inter-annual variability and a substantial suess Effect (the decrease in 14 C/ 12 C since 1900). The sargasso sea mixing rates between the surface and thermocline varied minimally over the past two centuries, despite changes to mean-hemispheric climate, including the Little Ice Age and variability in the north Atlantic oscillation. This result indicates that regional formation rates of sub-tropical mode water are stable over decades, and that anthropogenic carbon absorbed by the ocean does not return to the surface at a variable rate.

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“…Bermuda, a northernmost location for surface coral growth and near a site of high, deep sea sedimentation rates, has been the location for several reconstructions of past climate from coral [Draschba et al, 2000;Druffel, 1997;Kuhnert et al, 2005], foraminifera and alkenone based proxy reconstructions .…”

Section: Study Sitementioning

confidence: 99%

Geochemistry of slow-growing corals : reconstructing sea surface temperature, salinity and the North Atlantic Oscillation

Goodkin¹

2007

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A 225-year old coral from the south shore of Bermuda (64°W, 32 0 N) provides a record of decadal-to-centennial scale climate variability. The coral was collected live, and sub-annual density bands seen in x-radiographs delineate cold and warm seasons allowing for precise dating. Coral skeletons incorporate strontium (Sr) and calcium (Ca) in relative proportions inversely to the sea surface temperature (SST) in which the skeleton is secreted. 6180 of the coral skeleton changes based on both temperature and the 6180 of sea water ( 6 Ow), and 6Ow is proportional to sea surface salinity (SSS).Understanding long-term climate variability requires the reconstruction of key climate parameters, such as sea surface temperature (SST) and salinity, in records extending beyond the relatively short instrumental period. The high accretion rates, longevity, and skeletal growth bands found in coral skeletons make them an ideal resource for well-dated, seasonal climate reconstructions. Growing between 2 and 6 mm/year and reaching more than im in length, slowgrowing corals provide multi-century records from one colony. Additionally, unlike the fast growing (10-20 mm/year) species Porites, slow-growing species are generally found in both tropical and sub-tropical locations greatly expanding the geographical location of these records.A high resolution record (HRR, -11 samples per year) was drilled for the entire length of the coral record (218 years). Samples were split and Sr/Ca, 6180, and 61 3 C were measured for each sample. Sr/Ca was used to reconstruct winter time and mean-annual SST. Oxygen isotopic measurements were used to determine directional salinity changes, in conjunction with Sr/Ca based SST reconstructions. Winter-time and mean annual SSTs show SSTs -1.5 'C colder during the end of the Little Ice Age (LIA) relative to today. Simultaneously, SSS is fresher during that time.Sr/Ca based climate reconstructions from coral skeletons have been met with some skepticism because some reconstructions show temperature changes back in time that are 2-4 times greater than the reconstructions of other marine proxies. In this study, we show that when using bulk-sampled, slow-growing corals, two steps are critical to producing accurate reconstructions: 1) incorporating growth rate into multi-variant regressions with SST and Sr/Ca and 2) using multiple colonies that grew at the same time with varying average growth rates and Sr/Ca. Application of these novel methods over the period of the instrumental record from Hydrostation S (monthly since 1954, 32°10'N, 64°30'W) reduces the root mean square of the residuals between the reconstructed SST and the instrumental SST by as much as 1.52'C to 0.46 0 C for three coral colonies. Winter-time SSTs at Bermuda are correlated to phases of the North Atlantic Oscillation (NAO), a meridional oscillation in atmospheric mass. Much uncertainty remains about the relationship between the NAO and the ocean, and one critical outstanding question is whether anthropogenic changes are perturbing the ...

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NAO signature in a Bermuda coral Sr/Ca record

Cited by 40 publications

References 46 publications

Shifts in coral reef biogeochemistry and resulting acidification linked to offshore productivity

Shifts in coral reef biogeochemistry and resulting acidification linked to offshore productivity

Two centuries of limited variability in subtropical North Atlantic thermocline ventilation

Geochemistry of slow-growing corals : reconstructing sea surface temperature, salinity and the North Atlantic Oscillation

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