“…Approximately 20 mol m −2 of CO 2 has been taken up by the upper ocean at each of these study sitesFig. 3South Pacific coral δ 13 C and skeletal extension rate: coral annual skeletal extensions rates (in blue) and annual average skeletal δ 13 C (black open dots) and δ 13 C data with the average atmospheric 13 C Suess effect removed (solid black dots) in Porites lutea corals from: a Fiji core AB 53 , b Fiji core 1F 52 , c Tonga core TNI2 54 , d Rarotonga core 2R 51,52 , and e American Samoa core Ta’u-1 55,56 . Extension rate and δ 13 C significantly correlate to varying degrees (see R values in Table 1) up until the mid-20th century when coral δ 13 C abruptly shifts ~1.0‰ lower at all of these sites.…”
Section: Resultsmentioning
confidence: 99%
“…In November 2011, we cored a large colony of P. lutea on the western side of the island of Ta’u located at S 14° 15′ 33.74″: W 169° 30′ 01.61″ (or S 14 15.566, W 169 30.027) on an exposed outer reef in 7.5 m of water (water depth to top of coral) 55,56 . Prior to slabbing, the longest core, Tau-1, was scanned by X-ray computer automated tomography (CT) to reveal growth bands and to determine the optimal cutting planes (CT collage of coral cores in Tangri et al 56 ).…”
Section: Methodsmentioning
confidence: 99%
“…Below this section, annual δ 18 O minima and maximum were attributed to seasonal maxima and minima in SST, respectively. Verification of this approach comes from pseudo-coral forward modeling where we used instrumental SST and sea surface salinity (SSS) to generate a modeled coral δ 18 O series from 1981 to 2008 55 . The final chronology for Ta’u-1 based annual banding and annual δ 18 O cycles extends from 1521 to 2011 CE with an average extension rate of 1.2 cm yr −1 .…”
Although reef coral skeletal carbon isotopes (δ
13
C) are routinely measured, interpretation remains controversial. Here we show results of a consistent inverse relationship between coral δ
13
C and skeletal extension rate over the last several centuries in
Porites
corals at Fiji, Tonga, Rarotonga and American Samoa in the southwest Pacific. Beginning in the 1950s, this relationship breaks down as the atmospheric
13
C Suess effect shifts skeletal δ
13
C > 1.0‰ lower. We also compiled coral δ
13
C from a global array of sites and find that mean coral δ
13
C decreases by −1.4‰ for every 5 m increase in water depth (
R
= 0.68,
p
< 0.01). This highlights the fundamental sensitivity of coral δ
13
C to endosymbiotic photosynthesis. Collectively, these results suggest that photosynthetic rate largely determines mean coral δ
13
C while changes in extension rate and metabolic effects over time modulate skeletal δ
13
C around this mean value. The newly quantified coral δ
13
C-water depth relationship may be an effective tool for improving the precision of paleo-sea level reconstruction using corals.
“…Approximately 20 mol m −2 of CO 2 has been taken up by the upper ocean at each of these study sitesFig. 3South Pacific coral δ 13 C and skeletal extension rate: coral annual skeletal extensions rates (in blue) and annual average skeletal δ 13 C (black open dots) and δ 13 C data with the average atmospheric 13 C Suess effect removed (solid black dots) in Porites lutea corals from: a Fiji core AB 53 , b Fiji core 1F 52 , c Tonga core TNI2 54 , d Rarotonga core 2R 51,52 , and e American Samoa core Ta’u-1 55,56 . Extension rate and δ 13 C significantly correlate to varying degrees (see R values in Table 1) up until the mid-20th century when coral δ 13 C abruptly shifts ~1.0‰ lower at all of these sites.…”
Section: Resultsmentioning
confidence: 99%
“…In November 2011, we cored a large colony of P. lutea on the western side of the island of Ta’u located at S 14° 15′ 33.74″: W 169° 30′ 01.61″ (or S 14 15.566, W 169 30.027) on an exposed outer reef in 7.5 m of water (water depth to top of coral) 55,56 . Prior to slabbing, the longest core, Tau-1, was scanned by X-ray computer automated tomography (CT) to reveal growth bands and to determine the optimal cutting planes (CT collage of coral cores in Tangri et al 56 ).…”
Section: Methodsmentioning
confidence: 99%
“…Below this section, annual δ 18 O minima and maximum were attributed to seasonal maxima and minima in SST, respectively. Verification of this approach comes from pseudo-coral forward modeling where we used instrumental SST and sea surface salinity (SSS) to generate a modeled coral δ 18 O series from 1981 to 2008 55 . The final chronology for Ta’u-1 based annual banding and annual δ 18 O cycles extends from 1521 to 2011 CE with an average extension rate of 1.2 cm yr −1 .…”
Although reef coral skeletal carbon isotopes (δ
13
C) are routinely measured, interpretation remains controversial. Here we show results of a consistent inverse relationship between coral δ
13
C and skeletal extension rate over the last several centuries in
Porites
corals at Fiji, Tonga, Rarotonga and American Samoa in the southwest Pacific. Beginning in the 1950s, this relationship breaks down as the atmospheric
13
C Suess effect shifts skeletal δ
13
C > 1.0‰ lower. We also compiled coral δ
13
C from a global array of sites and find that mean coral δ
13
C decreases by −1.4‰ for every 5 m increase in water depth (
R
= 0.68,
p
< 0.01). This highlights the fundamental sensitivity of coral δ
13
C to endosymbiotic photosynthesis. Collectively, these results suggest that photosynthetic rate largely determines mean coral δ
13
C while changes in extension rate and metabolic effects over time modulate skeletal δ
13
C around this mean value. The newly quantified coral δ
13
C-water depth relationship may be an effective tool for improving the precision of paleo-sea level reconstruction using corals.
“…The δ 18 O‐NINO1+2 correlation was negative in the early twentieth century, consistent with warm and/or fresh (cool and/or salty) anomalies during El Niño (La Niña). This correlation also changed polarity beginning around 1930 (also see Linsley et al, ). We obtain similar results using the HadSST data set (Figure S6).…”
Section: Resultsmentioning
confidence: 84%
“…But the weak response to other ENSO events belies such a simple explanation. A comparison of the annually averaged Ta'u δ 18 O record with the NINO3.4 index over recent years (1981–2009) indicates a temporally varying and, on average, insignificant correlation (also see Linsley et al, ). This is expected based on the location of Ta'u in the current ENSO 3.4 null zone.…”
A 492‐year‐long, continuous δ18O time series from a massive Porites coral colony in Ta'u, American Samoa, records contrasting responses to different types of El Niño‐Southern Oscillation (ENSO) through a mixed sea surface temperature and salinity signal. Currently, conventional El Niño (La Niña) events generate cold and salty (warm and fresh) anomalies at Ta'u, while Modoki El Niño (La Niña) events warm (cool) the waters at Ta'u. Over the course of the twentieth century, the Ta'u δ18O record underwent a polarity shift in its response to conventional ENSO: A warm and fresh (cool and salty) response to El Niño (La Niña) was replaced by the opposite pattern. We interpret this as evidence for the movement of the Eastern Pacific ENSO null zone, the narrow band of the surface ocean where sea surface temperature variability is not on average correlated with ENSO. This movement appears to be related to overall shrinking of the ENSO footprint over the twentieth century. We infer no such trend in the Modoki footprint. The five‐century‐long Ta'u record shows dramatic, century‐scale changes in ENSO‐band variability. Comparisons with other ENSO reconstructions lead to conflicting interpretations: The Ta'u coral may have recorded changes in the strength of ENSO or in its spatial footprint. Changes in the spatial footprint manifest as a changing sensitivity to ENSO at any given location, presenting challenges to established methods of ENSO reconstruction.
The Great Barrier Reef (GBR) is an internationally recognized and widely studied ecosystem, yet little is known about its sea surface temperature (SST) evolution since the Last Glacial Maximum (LGM) (~20 kyr BP). Here, we present the first paleo‐application of Isopora coral‐derived SST calibrations to a suite of 25 previously published fossil Isopora from the central GBR spanning ~25–11 kyr BP. The resultant multicoral Sr/Ca‐ and δ18O‐derived SST anomaly (SSTA) histories are placed within the context of published relative sea level, reef sequence, and coralgal reef assemblage evolution. Our new calculations indicate SSTs were cooler on average by ~5–5.5°C at Noggin Pass (~17°S) and ~7–8°C at Hydrographer's Passage (~20°S) (Sr/Ca‐derived) during the LGM, in line with previous estimates (Felis et al., 2014, https://doi.org/10.1038/ncomms5102). We focus on contextualizing the Younger Dryas Chronozone (YDC, ~12.9–11.7 kyr BP), whose Southern Hemisphere expression, in particular in Australia, is elusive and poorly constrained. Our record does not indicate cooling during the YDC with near‐modern temperatures reached during this interval on the GBR, supporting an asymmetric hemispheric presentation of this climate event. Building on a previous study (Felis et al., 2014, https://doi.org10.1038/ncomms5102), these fossil Isopora SSTA data from the GBR provide new insights into the deglacial reef response, with near‐modern warming during the YDC, since the LGM.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
