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Introduction
Publications
Publications (115)
Ocean warming is killing corals, but heat-tolerant populations exist; if protected, they could replenish affected reefs naturally or through restoration. Palau’s Rock Islands experience consistently higher temperatures and extreme heatwaves, yet their diverse coral communities bleach less than those on Palau’s cooler outer reefs. Here, we combined...
Plain Language Summary
Mass bleaching events caused by warming oceans and intensifying marine heatwaves have killed millions of corals globally. In the central equatorial Pacific, coral reefs experienced three extreme heatwaves within 15 years, providing valuable insights into the mechanisms that could facilitate coral survival under global warming...
Plain Language Summary
Measurable anthropogenic‐induced acidification of the oceans (OA) has occurred over the last four decades. But its impact on coral reef ecosystems, such as coral calcification, has yet to be unambiguously demonstrated. This problem with detection and attribution of OA impacts is due, in large part, to the fact that multiple c...
Net ecosystem calcification (NEC) rates of Palau's largest lagoon and barrier reef system between 1992 and 2015 are estimated from sparse total alkalinity (TA) and salinity measurements and a tidal exchange model in which surface lagoon water transported offshore on the ebb tide is replaced by saltier (denser) ocean water that sinks to the bottom a...
Internal waves strongly influence the physical and chemical environment of coastal ecosystems worldwide. We report novel observations from a distributed temperature sensing (DTS) system that tracked the transformation of internal waves from the shelf break to the surf zone over a narrow shelf slope region in the South China Sea. The spatially conti...
Nutrient enrichment can slow growth, enhance bioerosion rates, and intensify algal competition for reef-building corals. In areas of high human population density and/or limited waste management, submarine groundwater discharge can transfer anthropogenic nutrients from polluted groundwater to coastal reefs. In this case study, we investigate the im...
Figure 2 in the original article has been updated with this figure 2 due to discrepancies related to incorrect mapping with one of the islands.
Ocean warming is negatively impacting coral reef ecosystems and considerable effort is currently invested in projecting coral reef futures under 21st century climate change. A limiting factor in these projections is lack of quantitative data on the thermal thresholds of different reef communities, due in large part to spatial and temporal gaps in b...
The Holocene is considered a period of relative climatic stability, but significant proxy data‐model discrepancies exist that preclude consensus regarding the postglacial global temperature trajectory. In particular, a mid‐Holocene Climatic Optimum, ~9,000 to ~5,000 years BP, is evident in Northern Hemisphere marine sediment records, but its absenc...
Internal waves can influence water properties in coastal ecosystems through the shoreward transport and mixing of subthermocline water into the nearshore region. In June 2014, a field experiment was conducted at Dongsha Atoll in the northern South China Sea to study the impact of internal waves on a coral reef. Instrumentation included a distribute...
The oceans are warming and coral reefs are bleaching with increased frequency and severity, fueling concerns for their survival through this century. Yet in the central equatorial Pacific, some of the world’s most productive reefs regularly experience extreme heat associated with El Niño. Here we use skeletal signatures preserved in long-lived cora...
Human alteration of the global nitrogen cycle intensified over the 1900s. Model simulations suggest that large swaths of the open ocean, including the North Atlantic and the western Pacific, have already been affected by anthropogenic nitrogen through atmospheric transport and deposition. Here we report an ∼130-year-long record of the ¹⁵N/¹⁴N of sk...
Laboratory-based CO2 experiments and studies of naturally low pH coral reef ecosystems reveal negative impacts of ocean acidification on the calcifying communities that build coral reefs. Conversely, in Palau's low pH lagoons, coral cover is high, coral communities are diverse, and calcification rates of two reef-building corals exhibit no apparent...
The skeletons of many reef-building corals are accreted with rhythmic structural patterns that serve as valuable sclerochronometers. Annual high- and low-density band couplets, visible in X-radiographs or computed tomography scans, are used to construct age models for paleoclimate reconstructions and to track variability in coral growth over time....
From air to shining sea
Nitrogen is an essential nutrient for phytoplankton growth. Nitrogen is primarily supplied to the surface ocean by mixing from below. However, as fertilizer use and combustion of fossil fuels rise, the atmosphere is expected to become an increasingly important source. Ren et al. measured nitrogen isotopes in organic matter f...
Coral barium to calcium (Ba/Ca) ratios have been used to reconstruct records of upwelling, river and groundwater discharge, and sediment and dust input to the coastal ocean. However, this proxy has not yet been explicitly tested to determine if Ba inclusion in the coral skeleton is directly proportional to seawater Ba concentration and to further d...
A 2 °C increase in global temperature above pre-industrial levels is considered a reasonable target for avoiding the most devastating impacts of anthropogenic climate change. In June 2015, sea surface temperature (SST) of the South China Sea (SCS) increased by 2 °C in response to the developing Pacific El Niño. On its own, this moderate, short-live...
Coral skeletons are valuable archives of past ocean conditions. However, interpretation of coral paleotemperature records is confounded by uncertainties associated with single element-ratio thermometers, including Sr/Ca. A new approach, Sr-U, uses U/Ca to constrain the influence of Rayleigh fractionation on Sr/Ca [DeCarlo et al., 2016]. Here, we bu...
Coral reefs are built of calcium carbonate (CaCO3) produced biogenically by a diversity of calcifying plants, animals, and microbes. As the ocean warms and acidifies, there is mounting concern that declining calcification rates could shift coral reef CaCO3 budgets from net accretion to net dissolution. We quantified net ecosystem calcification (NEC...
Fine scale temperature structures, which are commonly found in the top few meters of shallow water columns, may result in deviations of the remotely sensed night-time sea surface temperatures (SST) by the MODIS-Aqua sensor (SSTsat) from the bulk sea surface temperatures (SSTbulk) that they purport to represent. The discrepancies between SSTsat and...
coralCT was developed by T.M. DeCarlo in the Cohen Lab at Woods Hole Oceanographic Institution ( http://www.whoi.edu/cohenlab/ ) with funding from the National Science Foundation (NSF) grants OCE 1041106 and OCE 1220529, and an NSF Graduate Research Fellowship awarded to Thomas DeCarlo. coralCT is a MATLAB code for coral calcification and bioerosio...
Coral skeletons archive past climate variability with unrivaled temporal resolution. However, extraction of accurate temperature information from coral skeletons has been limited by “vital effects”, which confound, and sometimes override, the temperature dependence of geochemical proxies. We present a new approach to coral paleothermometry based on...
The isotopic composition of skeleton-bound organic nitrogen in shallow-water scleractinian corals (hereafter, CS-δ15N) is an emerging tool for studying the marine nitrogen cycle in the past. The CS-δ15N has been shown to reflect the δ15N of nitrogen (N) sources to corals, with most applications to date focusing on the anthropogenic/terrestrial N in...
There are concerns about the future of coral reefs in the face of ocean acidification and warming, and although studies of
these phenomena have advanced quickly, efforts have focused on pieces of the puzzle rather than integrating them to evaluate
ecosystem-level effects. The field is now poised to begin this task, but there are information gaps th...
Global climate models (GCMs) predict enhanced warming and nutrient decline across the central tropical Pacific as trade winds weaken with global warming. Concurrent changes in circulation, however, have potential to mitigate these effects for equatorial islands. The implications for densely populated island nations, whose livelihoods depend on ecos...
Coral Sr/Ca is widely used to reconstruct past ocean temperatures. However, some studies report different Sr/Ca-temperature relationships for conspecifics on the same reef, with profound implications for interpretation of reconstructed temperatures. We assess whether these differences are attributable to small-scale oceanographic variability or “vi...
Ocean acidification threatens the survival of coral reef ecosystems worldwide. The negative effects of ocean acidification observed in many laboratory experiments have been seen in studies of naturally low-pH reefs, with little evidence to date for adaptation. Recently, we reported initial data suggesting that low-pH coral communities of the Palau...
Coastal ocean ecosystems have always served human populations—they provide food security, livelihoods, coastal protection, and defense. Ocean acidification is a global threat to these ecosystem services, particularly when other local and regional stressors combine with it to jeopardize coastal health. Monitoring efforts call for a coordinated globa...
The U/Ca ratio of aragonite coral skeleton exhibits coherent patterns of seasonal and interannual variability. In field-sampled corals and those grown in controlled culture experiments, strong correlations have been found between coral skeleton U/Ca and water temperature, pH, carbonate ion concentration, and salinity. However, the mechanism(s) unde...
Coral reefs exist in a delicate balance between calcium carbonate (CaCO3) production and CaCO3 loss. Ocean acidification (OA), the CO2-driven decline in seawater pH and CaCO3 saturation state (Ω), threatens to tip this balance by decreasing calcification, and increasing erosion and dissolution. While multiple CO2 manipulation experiments show coral...
:[1] Anthropogenic carbon dioxide emissions are acidifying the oceans, reducing the concentration of carbonate ions ([CO32-]) that calcifying organisms need to build and cement coral reefs. To date, studies of a handful of naturally acidified reef systems reveal depauperate communities, sometimes with reduced coral cover and calcification rates, co...
The skeleton-bound organic nitrogen in reef-building symbiotic corals may be a high-resolution archive of ocean nitrogen cycle dynamics and a tool for understanding coral biogeochemistry and physiological processes. However, the existing methods for measuring the isotopic composition of coral skeleton-bound organic nitrogen (hereafter, CS-δ15N) eit...
Oxygen isotope fractionation factors between aragonite and seawater are studied at T = 25–55 °C and pH = 7.4–8.1 in a set of ‘free-drift’ precipitation experiments with various CO2-degassing rates (0–75 cc/min). The measured fractionation factors correlate weakly with degassing rate, but strongly with temperature in the following form (R2 = 0.998):...
Ocean acidification (OA) threatens the existence of coral reefs by slowing the rate of calcium carbonate (CaCO3) production of framework-building corals thus reducing the amount of CaCO3 the reef can produce to counteract natural dissolution. Some evidence exists to suggest that elevated levels of dissolved inorganic nutrients can reduce the impact...
In situ secondary ion mass spectrometry (SIMS) analyses of δ7Li, Li/Ca, and Mg/Ca were performed on five synthetic aragonite samples precipitated from seawater at 25°C at different rates. The compositions of δ7Li in bulk aragonites and experimental fluids were measured by multicollector inductively coupled plasma–mass spectrometry (MC-ICP-MS). Both...
As the surface ocean equilibrates with rising atmospheric CO2, the pH of surface seawater is decreasing with potentially negative impacts on coral calcification. A critical question is whether corals will be able to adapt or acclimate to these changes in seawater chemistry. We use high precision CT scanning of skeletal cores of Porites astreoides,...
Anthropogenic carbon dioxide (CO2) is being absorbed into the ocean, altering seawater chemistry, with potentially negative impacts on a wide range of marine organisms. The early life stages of invertebrates with internal and external aragonite structures may be particularly vulnerable to this ocean acidification. Impacts to cephalopods, which form...
Ocean acidification, characterized by elevated pCO2 and the associated decreases in seawater pH and calcium carbonate saturation state (Ω), has a variable impact on the growth and survival of marine invertebrates. Larval stages are thought to be particularly vulnerable to environmental stressors, and negative impacts of ocean acidification have bee...
Continuous exposure to decreased pH and CaCO3 saturation state has been shown to have detrimental effects on bivalve larvae, but the mechanisms behind these responses are largely unknown, and it is unknown whether CO2-exposure during early life stages is critical to later development. We hypothesize that the CO2 condition experienced during initial...
The detectable magnesium (Mg) isotope fractionation between biogenic aragonite (including aragonitic corals, bivalves, scaphopod, and sclerosponges) and seawater can potentially be applied to reconstruct sea surface temperature (SST) in the past. To calibrate this thermometer, eight sets of inorganic precipitation experiments (‘free-drift’) in seaw...
In situ skeletal markers have been widely used to quantify skeletal growth rates of scleractinian corals on sub-annual time-scales. Nevertheless, an evaluation of different techniques, both in terms of their efficacy and potential impacts on the growth process itself, has not been undertaken. Here the effects of exposure to four different dyes (ali...
Accurate low-latitude sea surface temperature (SST) records that predate the instrumental era are needed to put recent warming in the context of natural climate variability, and to evaluate the persistence of lower frequency climate variability prior to the instrumental era and the possible influence of anthropogenic climate change on this variabil...
Anthropogenic ocean acidification is likely to have negative effects on marine calcifying organisms, such as shelled pteropods, by promoting dissolution of aragonite shells. Study of shell dissolution requires an accurate and sensitive method for assessing shell damage. Shell dissolution was induced through incubations in CO2‐enriched seawater for...
Upwelling across the tropical Pacific Ocean is projected to weaken in
accordance with a reduction of the atmospheric overturning circulation,
enhancing the increase in sea surface temperature relative to other
regions in response to greenhouse-gas forcing. In the central Pacific,
home to one of the largest marine protected areas and fishery regions...
Marine invertebrates are particularly vulnerable to environmental stressors during larval development. Continuous exposure to decreased pH and CaCO3 saturation state, known as ocean acidification (OA), has been shown to have detrimental effects on bivalve larvae. However, bivalve larvae developing in coastal and estuarine systems likely encounter h...
The effects of nutrients and pCO2 on zooxanthellate and
azooxanthellate colonies of the temperate scleractinian coral Astrangia
poculata (Ellis and Solander, 1786) were investigated at two different
temperatures (16 °C and 24 °C). Corals exposed to elevated
pCO2 tended to have lower relative calcification rates, as
estimated from changes in buoyant...
Coral reef ecosystems are currently threatened by anthropogenic loading
of CO2 to the atmosphere and global surface oceans. Model predictions
and laboratory experiments indicate that as the pH of the oceans drops,
the ability of calcifying corals to build their carbonate skeletons will
be significantly reduced. Here, we investigate coral calcificat...
The barium/calcium ratio (Ba/Ca) in corals growing on fringing reefs of
the Yucatan Peninsula is a potentially powerful tool with which to
reconstruct seasonally resolved, multicentury-long records of
precipitation (both seasonally-forced as well as episodic events). The
Yucatan Peninsula is a carbonate platform with minimal surface flow,
thus grou...
Observational and modeling studies have shown that long term North
Atlantic basin-averaged sea surface temperatures (SSTs) combine a
CO2-forced global warming trend with a multi-decadal oscillation (the
Atlantic Multidecadal Oscillation or AMO) that likely arose from
internal variability. The AMO can mitigate or amplify regional climate
change, and...
The integrity of coral-based reconstructions of past climate variability depends on a comprehensive knowledge of the effects of post-depositional alteration on coral skeletal geochemistry. Here we combine millimeter-scale and micro-scale coral Sr/Ca data, scanning electron microscopy (SEM) images, and X-ray diffraction with previously published δ18...
Rates of calcium carbonate (CaCO3) production by reef calcifying organisms (predominantly scleractinian corals and coralline algae) must exceed rates of CaCO3 loss via dissolution and sediment transport, if coral reefs are to persist and grow. Historically, constructive and destructive processes have been closely balanced – with net reef accumulati...
Background/Question/Methods
There is increasing evidence that sea surface warming trends are causing unequivocal impacts on coral reef ecosystems at a planetary scale. Sea surface temperature (SST) has shown a significant increase over the last few decades across circumtropical oceans. Impacts have included significant % coral cover decline, decli...
Many physiological responses in present-day coral reefs to climate change are interpreted as consistent with the imminent
disappearance of modern reefs globally because of annual mass bleaching events, carbonate dissolution, and insufficient time
for substantial evolutionary responses. Emerging evidence for variability in the coral calcification re...
Rising concentrations of atmospheric CO2 are changing the carbonate chemistry of the oceans, a process known as ocean acidification (OA). Absorption of this CO2 by the surface oceans is increasing the amount of total dissolved inorganic carbon (DIC) and bicarbonate ion (HCO3
−) available for marine calcification yet is simultaneously lowering the s...
Western subtropical North Atlantic oceanic and atmospheric circulations
connect tropical and subpolar climates. Variations in these circulations
can generate regional climate anomalies that are not reflected in
Northern Hemisphere averages. Assessing the significance of
anthropogenic climate change at regional scales requires proxy records
that all...
This study presents a new approach to coral thermometry that deconvolves the influence of water temperature on skeleton composition from that of “vital effects”, and has the potential to provide estimates of growth temperatures that are accurate to within a few tenths of a degree Celsius from both tropical and cold-water corals. Our results provide...
Anthropogenic elevation of atmospheric pCO2 is predicted to cause the pH of surface seawater to decline by 0.3–0.4 units by 2100 AD, causing a 50% reduction in seawater
[CO3
2−] and undersaturation with respect to aragonite in high-latitude surface waters. We investigated the impact of CO2-induced ocean acidification on the temperate scleractinian...
Sea surface temperature (SST) across much of the tropics has increased by 0.4° to 1°C since the mid-1970s. A parallel increase
in the frequency and extent of coral bleaching and mortality has fueled concern that climate change poses a major threat to
the survival of coral reef ecosystems worldwide. Here we show that steadily rising SSTs, not ocean...
Zooxanthellate colonies of the scleractinian coral Astrangia poculata were grown under combinations of ambient and elevated nutrients (5 μM NO3-, 0.3 μM PO4- 3, and 2 nM Fe+ 2) and CO2 (∼ 780 ppmv) treatments for a period of 6 months. Coral calcification rates, estimated from buoyant weights, were not significantly affected by moderately elevated n...
Much of our understanding of Earth's climate history is based on interpretation of geochemical variability within the CaCO3 tests and skeletons of marine organisms. Geochemical climate proxies are typically cast in terms of equilibrium thermodynamics, but there are important differences between the compositions of carbonates accreted by living orga...