Central Tropical Pacific Research Articles

Constraints on the salinity–oxygen isotope relationship in the central tropical Pacific Ocean

Uncertainties surround the relationship between salinity and the stable isotopic composition of seawater, largely due to a dearth of modern seawater isotope data. Here we report 191 new, paired measurements of salinity and seawater oxygen isotopes (δ18Osw) taken from the central tropical Pacific in May 2012, from the surface to 4600m depth. We observe significant correlations between δ18Osw and salinity across the study region, with slopes ranging from 0.23 to 0.31‰/psu for the mixed layer, and 0.35–0.42‰/psu for waters between the mixed layer and 500m depth. When considering δ18Osw–salinity across averages of individual water masses in the region, slopes range from 0.21 to 0.40‰/psu, albeit with appreciable scatter. Surface salinity and δ18Osw data corresponding to the North Equatorial Countercurrent are significantly higher than previously observed, which we attribute to a weak westerly current and dry conditions in the region during the May 2012 cruise. Subsurface (80–500m) salinity values from 2012 are significantly lower than corresponding values from pre-existing regional data, highlighting a different latitudinal sampling distribution, while subsurface δ18Osw is not significantly different. Thus, in May 2012, δ18Osw in this region could not be used to distinguish between subsurface water masses of different salinities. Unlike other regions where the surface ‘freshwater endmember’ is close to the δ18O value of regional precipitation, the freshwater endmember implied by our dataset (−10.38‰) is consistent with a strong evaporative influence. Paired δ18O–δD values of precipitation and surface seawaters have similar slopes (5.0, 5.1), and relatively low intercepts (1.4, 0.8) indicating isotopic variability in both reservoirs is also partly controlled by evaporation.

Change in surface latent heat flux and its association with tropical cyclone genesis in the western North Pacific

The present study investigates the influence of June through November (JJASON) thermal state of the western North Pacific warm pool on surface latent heat flux and their association with tropical cyclone (TC) genesis by using 25 level water temperature data with European Centre for Medium-Range Weather Forecasts (ECWMF) operational ocean analysis (ORA-S3), the monthly mean fluxes from Objectively Analyzed Air-sea Fluxes (OAFlux) Project, and the tropical cyclone data from the International Best Track Archive for Climate Stewardship (IBTrACS). It is found that positive (negative) latent heat flux anomalies over the western North Pacific are associated with warm (cold) state of the warm pool. The analysis suggests that the change in sea-air humidity difference has a direct contribution to surface latent heat flux anomalies over the western Pacific in warm state years of the warm pool. However, the change in surface wind speed is the main cause of surface latent heat flux anomalies over central tropical Pacific. In cold state years, change in the sea-air humidity difference has a direct contribution to surface latent heat flux anomalies over the western Pacific and central and eastern tropical Pacific, and the change in surface wind speed appears not to be a cause of identified surface latent heat flux anomalies. Moreover, the results show that the sea-air humidity difference contributes to tropical cyclone genesis in warm state years, but in cold state years, tropical cyclone genesis occurs mainly in regions of sea-air humidity difference decrease and surface wind speed increase.

Ocean chlorophyll response to two types of El Niño events in an ocean‐biogeochemical coupled model

AbstractBased on a long‐term simulation of an ocean‐biogeochemical coupled model, we investigate the biogeochemical response to the two types of El Niño events, a Cold Tongue (CT)‐El Niño and a Warm Pool (WP)‐El Niño, in which a local maximum of anomalous sea surface temperature (SST) is located in the eastern and central tropical Pacific. Our model is able to reasonably simulate the characteristics of the biological variables in a way comparable to the observations. During the developing period, anomalous low chlorophyll appears in the eastern Pacific, while it appears in the central Pacific in the WP‐El Niño. The difference in the spatial‐temporal response of chlorophyll for the two types of El Niño events is mainly due to the eastward zonal advection of upper ocean currents, which plays a role in bringing nutrient‐poor water from the western Pacific. During the decaying period of the WP‐El Niño, anomalous high chlorophyll appears concurrently with anomalous low SST in the eastern Pacific. Conversely, anomalous high chlorophyll appears in the central Pacific prior to the decaying period of the CT‐El Niño. In particular, the anomalous low sea level from the northwestern Pacific shifts to the southern equatorial region during the decaying period of the CT‐El Niño. This drives anticyclonic boundary currents which enhance the Equatorial Undercurrent, playing a role in the supply of nutrients to the central equatorial Pacific, resulting in an increase in chlorophyll concentration in the same region.

ENSO regimes and the late 1970's climate shift: The role of synoptic weather and South Pacific ocean spiciness

South Pacific subtropical density compensated temperature and salinity (spiciness) anomalies are known to be associated with decadal equatorial variability, however, the mechanisms by which such disturbances are generated, advect and the degree to which they modulate the equatorial thermocline remains controversial. During the late 1970's a climate regime transition preceded a period of strong and sustained El Nino events. Using an ocean general circulation model forced by the constituent mechanical and thermodynamic components of the reanalysed atmosphere we show that the late 1970's transition coincided with the arrival of a large-scale, subsurface cold and fresh water anomaly in the central tropical Pacific. An ocean reanalysis for the period 1990–2007 that assimilates subsurface Argo, XBT and CTD data, reveals that disturbances occur due to the subduction of negative surface salinity anomalies from near 30° S, 100° W which are advected along the σ=25–26 kgm−3 isopycnal surfaces. These anomalies take, on average, seven years to reach the central equatorial Pacific where they may substantially perturb the thermocline before the remnants ultimately ventilate in the region of the western Pacific warm pool. Positive (warm–salty) disturbances, known to occur due to late winter diapycnal mixing and isopycnal outcropping, arise due to both subduction of subtropical mode waters and subsurface injection. On reaching the equatorial band (10° S–0° S) these disturbances tend to deepen the thermocline reducing the model's ENSO. In contrast the emergence of negative (cold–fresh) disturbances at the equator are associated with a shoaling of the thermocline and El Nino events. Process studies are used to show that the generation and advection of anomalous density compensated thermocline disturbances critically depend on stochastic forcing of the intrinsic ocean by weather. We further show that in the absence of the inter-annual component of the atmosphere forcing Central Pacific El Nino events are manifest.

Ocean noise in the tropical and subtropical Pacific Ocean

Ocean ambient noise is well studied in the North Pacific and North Atlantic but is poorly described for most of the worlds' oceans. Calibrated passive acoustic recordings were collected during 2009-2010 at seven locations in the central and western tropical and subtropical Pacific. Monthly and hourly mean power spectra (15-1000 Hz) were calculated in addition to their skewness, kurtosis, and percentile distributions. Overall, ambient noise at these seven sites was 10-20 dB lower than reported recently for most other locations in the North Pacific. At frequencies <100 Hz, spectrum levels were equivalent to those predicted for remote or light shipping. Noise levels in the 40 Hz band were compared to the presence of nearby and distant ships as reported to the World Meteorological Organization Voluntary Observing Ship Scheme (VOS) project. There was a positive, but nonsignificant correlation between distant shipping and low frequency noise (at 40 Hz). There was a seasonal variation in ambient noise at frequencies >200 Hz with higher levels recorded in the winter than in the summer. Several species of baleen whales, humpback (Megaptera novaeangliae), blue (Balaenoptera musculus), and fin (B. physalus) whales, also contributed seasonally to ambient noise in characteristic frequency bands.

North-Central Pacific Tropical Cyclones: Impacts of El Niño–Southern Oscillation and the Madden–Julian Oscillation

Abstract Both El Niño–Southern Oscillation (ENSO) and the Madden–Julian oscillation (MJO) have been documented in previous research to impact tropical cyclone (TC) activity around the globe. This study examines the relationship of each mode individually along with a combined index on tropical cyclone activity in the north-central Pacific. Approximately twice as many tropical cyclones form in the north-central Pacific in El Niño years compared with La Niña years. These differences are attributed to a variety of factors, including warmer sea surface temperatures, lower sea level pressures, increased midlevel moisture, and anomalous midlevel ascent in El Niño years. When the convectively enhanced phase of the MJO is located over the eastern and central tropical Pacific, the north-central Pacific tends to have more tropical cyclone activity, likely because of reduced vertical wind shear, lower sea level pressures, and increased vertical motion. The convectively enhanced phase of the MJO is also responsible for most of the TCs that undergo rapid intensification in the north-central Pacific. A combined MJO–ENSO index that is primarily associated with anomalous rising motion over the tropical eastern Pacific has an even stronger relationship with north-central Pacific TCs, as well as rapid intensification, than either individually.

Comparing historical and modern methods of sea surface temperature measurement – Part 2: Field comparison in the central tropical Pacific

Abstract. Discrepancies between historical sea surface temperature (SST) datasets have been partly ascribed to use of different adjustments to account for variable measurement methods. Until recently, adjustments had only been applied to bucket temperatures from the late 19th and early 20th centuries, with the aim of correcting their supposed coolness relative to engine cooling water intake temperatures. In the UK Met Office Hadley Centre SST 3 dataset (HadSST3), adjustments have been applied over its full duration to observations from buckets, buoys and engine intakes. Here we investigate uncertainties in the accuracy of such adjustments by direct field comparison of historical and modern methods of shipboard SST measurement. We compare wood, canvas and rubber bucket temperatures to 3 m seawater intake temperature along a central tropical Pacific transect conducted in May and June 2008. We find no average difference between the temperatures obtained with the different bucket types in our short measurement period (∼1 min). Previous field, lab and model experiments have found sizeable temperature change of seawater samples in buckets of smaller volume under longer exposure times. We do, however, report the presence of strong near-surface temperature gradients day and night, indicating that intake and bucket measurements cannot be assumed equivalent in this region. We thus suggest bucket and buoy measurements be considered distinct from intake measurements due to differences in sampling depth. As such, we argue for exclusion of intake temperatures from historical SST datasets and suggest this would likely reduce the need for poorly field-tested bucket adjustments. We also call for improvement in the general quality of intake temperatures from Voluntary Observing Ships. Using a physical model we demonstrate that warming of intake seawater by hot engine room air is an unlikely cause of overly warm intake temperatures. We suggest that reliable correction for such warm errors is not possible since they are largely of unknown origin and can be offset by real near-surface temperature gradients.

The MJO and global warming: a study in CCSM4

The change in Madden–Julian oscillation (MJO) amplitude and variance in response to anthropogenic climate change is assessed in the 1° nominal resolution community climate system model, version 4 (CCSM4), which has a reasonable representation of the MJO characteristics both dynamically and statistically. The twentieth century CCSM4 run is compared with the warmest twenty-first century projection (representative concentration pathway 8.5, or RCP8.5). The last 20 years of each simulation are compared in their MJO characteristics, including spatial variance distributions of winds, precipitation and outgoing longwave radiation, histograms of event amplitude, phase and duration, and composite maps of phases. The RCP8.5 run exhibits increased variance in intraseasonal precipitation, larger-amplitude MJO events, stronger MJO rainfall in the central and eastern tropical Pacific, and a greater frequency of MJO occurrence for phases corresponding to enhanced rainfall in the Indian Ocean sector. These features are consistent with the concept of an increased magnitude for the hydrological cycle under greenhouse warming conditions. Conversely, the number of active MJO days decreases and fewer weak MJO events occur in the future climate state. These results motivate further study of these changes since tropical rainfall variability plays such an important role in the region’s socio-economic well being.

Global ocean surface velocities from drifters: Mean, variance, El Niño–Southern Oscillation response, and seasonal cycle

Global near‐surface currents are calculated from satellite‐tracked drogued drifter velocities on a 0.5° × 0.5° latitude‐longitude grid using a new methodology. Data used at each grid point lie within a centered bin of set area with a shape defined by the variance ellipse of current fluctuations within that bin. The time‐mean current, its annual harmonic, semiannual harmonic, correlation with the Southern Oscillation Index (SOI), spatial gradients, and residuals are estimated along with formal error bars for each component. The time‐mean field resolves the major surface current systems of the world. The magnitude of the variance reveals enhanced eddy kinetic energy in the western boundary current systems, in equatorial regions, and along the Antarctic Circumpolar Current, as well as three large “eddy deserts,” two in the Pacific and one in the Atlantic. The SOI component is largest in the western and central tropical Pacific, but can also be seen in the Indian Ocean. Seasonal variations reveal details such as the gyre‐scale shifts in the convergence centers of the subtropical gyres, and the seasonal evolution of tropical currents and eddies in the western tropical Pacific Ocean. The results of this study are available as a monthly climatology.

Relative importance of tropical SST anomalies in forcing East Asian summer monsoon circulation

The relative importance of tropical SST anomalies to the dominant variability of East Asian Summer Monsoon (EASM) circulation is investigated using an atmospheric general circulation model and a linear inverse model. It is found that the cooling over the central tropical Pacific is crucial in developing and maintaining the summertime northwest Pacific anticyclones, associated with the EASM precipitation. In this regard, the previously suggested El Niño event in the preceding winter and accompanying tropical Indian Ocean warming alone may not be enough to predict the strength of EASM circulation. Instead, monitoring and predicting the evolution of sea surface temperature anomalies in the central tropical Pacific, especially in spring to summer, may greatly improve the prediction of EASM circulation.

Foraging of seabirds on pelagic fishes: implications for management of pelagic marine protected areas

Scientists and managers have become increasingly interested in how pelagic marine protected areas (PMPAs), or protected areas away from the coast, can be used to protect pelagic species. Subsurface-predator facilitated foraging ('facilitated foraging') between seabirds and subsurface predators, such as tunas, is a key ecological interaction in the tropical oceans where a number of large PMPAs have been created. In facilitated foraging, subsurface predators drive for- age fish to the surface, where they are made available to seabirds. Because this is a critical inter- action for seabirds, a reduction or cessation of fishing effort within tropical PMPAs may increase subsurface predator density, resulting in more foraging opportunities for seabirds closer to colonies. This interaction is well documented in the Eastern Tropical Pacific, and to a lesser extent in the Indian Ocean, but is poorly studied in the Central Tropical Pacific. Here, we review our cur- rent state of knowledge of facilitated foraging, particularly in relation to questions critical to PMPA management. We specifically consider 2 components of the foraging ecology of tropical seabird species: (1) diet and foraging methods, including flock feeding behavior, i.e. how species forage in association with other species or conspecifics, and (2) association with subsurface pred- ators. We consider the spatial scale of this interaction as it pertains to the distribution of seabirds and tunas and to PMPA boundaries. We conclude with discussion of data gaps and the implica- tions for managers. The present review of facilitated foraging will help focus future efforts and multidisciplinary collaborations on this important but understudied interaction.

Interdecadal enhancement of the walker circulation over the Tropical Pacific in the late 1990s

The Walker circulation is one of the major components of the large-scale tropical atmospheric circulation and variations in its strength are critical to equatorial Pacific Ocean circulation. It has been argued in the literature that during the 20th century the Walker circulation weakened, and that this weakening was attributable to anthropogenic climate change. By using updated observations, we show that there has been a rapid interdecadal enhancement of the Walker circulation since the late 1990s. Associated with this enhancement is enhanced precipitation in the tropical western Pacific, anomalous westerlies in the upper troposphere, descent in the central and eastern tropical Pacific, and anomalous surface easterlies in the western and central tropical Pacific. The characteristics of associated oceanic changes are a strengthened thermocline slope and an enhanced zonal SST gradient across the tropical Pacific. Many characteristics of these changes are similar to those associated with the mid-1970s climate shift with an opposite sign. We also show that the interdecadal variability of the Walker circulation in the tropical Pacific is inversely correlated to the interdecadal variability of the zonal circulation in the tropical Atlantic. An enhancement of the Walker circulation in the tropical Pacific is associated with a weakening zonal circulation in the tropical Atlantic and vise versa, implying an inter-Atlantic-Pacific connection of the zonal overturning circulation variation. Whether these recent changes will be sustained is not yet clear, but our research highlights the importance of understanding the interdecadal variability, as well as the long-term trends, that influence tropical circulation.

Slowdown of the Walker circulation driven by tropical Indo-Pacific warming

Global mean sea surface temperature (SST) has risen steadily over the past century, but the overall pattern contains extensive and often uncertain spatial variations, with potentially important effects on regional precipitation. Observations suggest a slowdown of the zonal atmospheric overturning circulation above the tropical Pacific Ocean (the Walker circulation) over the twentieth century. Although this change has been attributed to a muted hydrological cycle forced by global warming, the effect of SST warming patterns has not been explored and quantified. Here we perform experiments using an atmospheric model, and find that SST warming patterns are the main cause of the weakened Walker circulation over the past six decades (1950-2009). The SST trend reconstructed from bucket-sampled SST and night-time marine surface air temperature features a reduced zonal gradient in the tropical Indo-Pacific Ocean, a change consistent with subsurface temperature observations. Model experiments with this trend pattern robustly simulate the observed changes, including the Walker circulation slowdown and the eastward shift of atmospheric convection from the Indonesian maritime continent to the central tropical Pacific. Our results cannot establish whether the observed changes are due to natural variability or anthropogenic global warming, but they do show that the observed slowdown in the Walker circulation is presumably driven by oceanic rather than atmospheric processes.

A change in the relationship between tropical central Pacific SST variability and the extratropical atmosphere around 1990

A newly released reanalysis dataset covering the period 1979–2009 is analyzed to show that the sea surface temperature (SST) variability in the tropical central Pacific is more closely related to the SST variability in the tropical eastern Pacific before 1990 but more closely related to sea level pressure (SLP) variations associated with the North Pacific Oscillation (NPO) after 1990. Only during the period after 1990 can the NPO excite large SST variability in the tropical central Pacific. Related to this change, El Niño Southern Oscillation (ENSO) SST anomalies tend to spread from the eastern to central tropical Pacific before 1990 in a pattern resembling that associated with the Eastern Pacific (EP) type of ENSO, but are more closely connected to SST variability in the subtropical north Pacific after 1990 with a pattern resembling that of the Central Pacific (CP) type of ENSO. This study concludes that the increased influence of the NPO on the tropical Pacific is a likely reason for the increasing occurrence of the CP type of ENSO since 1990. An analysis of the mean atmospheric circulation during these two periods suggests that the increased NPO influence is associated with a strengthening Hadley circulation after 1990.

Impacts of non‐canonical El Niño patterns on Atlantic hurricane activity

The impact of non‐canonical El Niño patterns, typically characterized by warmer than normal sea surface temperatures (SSTs) in the central tropical Pacific, on Atlantic tropical cyclone (TC) is explored by using composites of key Atlantic TC indices and tropospheric vertical wind shear over the Atlantic main development region (MDR). The highlight of our major findings is that, while the canonical El Niño pattern has a strong suppressing influence on Atlantic TC activity, non‐canonical El Niño patterns considered in this study, namely central Pacific warming, El Niño Modoki, positive phase Trans‐Niño, and positive phase Pacific meridional mode, all have insubstantial impact on Atlantic TC activity. This result becomes more conclusive when the impact of MDR SST is removed from the Atlantic TC indices and MDR wind shear by using the method of linear regression. Further analysis suggests that the tropical Pacific SST anomalies associated with the non‐canonical El Niño patterns are not strong enough to cause a substantial warming of the tropical troposphere in the Atlantic region, which is the key factor that increases the wind shear and atmospheric static stability over the MDR. During the recent decades, the non‐canonical El Niños have been more frequent while the canonical El Niño has been less frequent. If such a trend continues in the future, it is expected that the suppressing effect of El Niño on Atlantic TC activity will diminish and thus the MDR SST will play a more important role in controlling Atlantic TC activity in the coming decades.

Understanding the responses of sea surface temperature to the two different types of El Niño in the western North Pacific

In this study, we examine the physical processes of the response of sea surface temperature (SST) in the western North Pacific to the two different types of El Niño, the Central Pacific El Niño and the Eastern Pacific El Niño. While a center of anomalous warm SST is observed in the eastern tropical Pacific in the case of the Eastern Pacific El Niño, it is located in the central tropical Pacific for the Central Pacific El Niño. We investigate the detailed SST response in the Kuroshio Extension region, where the anomalous SST is warm (cool) in the Central Pacific El Niño (Eastern Pacific El Niño) during the boreal fall and winter. We diagnose the SST tendency to identify the roles of the surface net heat fluxes and Ekman transport.During the fall and winter, the atmospheric teleconnections over the North Pacific are quite different between the two types of El Niño, which might be due to changes in atmospheric diabatic forcing in relation to rainfall in the tropical Pacific. Our results suggest that the physical processes, which are responsible for the western North Pacific SST in response to the two different types of El Niño, are basically similar. That is, Ekman heat transport plays a key role in warming and cooling of the SST anomalies in the Kuroshio Extension region in the Central Pacific El Niño and Eastern Pacific El Niño, respectively. In contrast, the net surface heat fluxes act to weaken the SST anomalies. This result indicates that changes in the anomalous atmospheric circulation over the North Pacific, which is directly associated with Ekman currents at the upper levels, are important to determine the responses of SST in the Kuroshio Extension region to the two types of El Niño.

Quantifying the residual effects of ENSO on low‐frequency variability in the tropical Pacific

AbstractThe asymmetry of El Niño‐La Niña, one of the well‐known characteristics of the El Niño‐Southern Oscillation (ENSO), is suggested to produce a non‐zero residual effect that could rectify the background state, and thereby generates the low‐frequency variability in the tropical Pacific. So far, this rectification effect has been hardly quantified apart from the low‐frequency variability because the low‐frequency variability captured via conventional methods represents the mixture of both the residual effects of ENSO and the no‐ENSO‐related natural decadal variability. Here we separate the residual effects of ENSO from the natural decadal variability that appears in four historical sea surface temperature datasets during the last century by applying a long‐term moving average. A significant correlation between the computed residual effect and the decadal change in the ENSO skewness (i.e. the measure of the El Niño‐La Niña asymmetry) confirmed the applicability of our computational method. Quantitatively, the residual effects of ENSO consistently account for at least 15% of the total low‐frequency variability in four datasets, especially over the eastern and central tropical Pacific. This implies that the asymmetry of ENSO enhances the tropical Pacific decadal variability for the last century. Copyright © 2012 Royal Meteorological Society

Tropical forcing of Circumpolar Deep Water Inflow and outlet glacier thinning in the Amundsen Sea Embayment, West Antarctica

AbstractOutlet glaciers draining the Antarctic ice sheet into the Amundsen Sea Embayment (ASE) have accelerated in recent decades, most likely as a result of increased melting of their ice-shelf termini by warm Circumpolar Deep Water (CDW). An ocean model forced with climate reanalysis data shows that, beginning in the early 1990s, an increase in westerly wind stress near the continental shelf edge drove an increase in CDW inflow onto the shelf. The change in local wind stress occurred predominantly in fall and early winter, associated with anomalous high sea-level pressure (SLP) to the north of the ASE and an increase in sea surface temperature (SST) in the central tropical Pacific. The SLP change is associated with geopotential height anomalies in the middle and upper troposphere, characteristic of a stationary Rossby wave response to tropical SST forcing, rather than with changes in the zonally symmetric circulation. Tropical Pacific warming similar to that of the 1990s occurred in the 1940s, and thus is a candidate for initiating the current period of ASE glacier retreat.

Pacific climate variability and the possible impact on global surface CO2 flux.

BackgroundClimate variability modifies both oceanic and terrestrial surface CO2 flux. Using observed/assimilated data sets, earlier studies have shown that tropical oceanic climate variability has strong impacts on the land surface temperature and soil moisture, and that there is a negative correlation between the oceanic and terrestrial CO2 fluxes. However, these data sets only cover less than the most recent 20 years and are insufficient for identifying decadal and longer periodic variabilities. To investigate possible impacts of interannual to interdecadal climate variability on CO2 flux exchange, the last 125 years of an earth system model (ESM) control run are examined.ResultsGlobal integration of the terrestrial CO2 flux anomaly shows variation much greater in amplitude and longer in periodic timescale than the oceanic flux. The terrestrial CO2 flux anomaly correlates negatively with the oceanic flux in some periods, but positively in others, as the periodic timescale is different between the two variables. To determine the spatial pattern of the variability, a series of composite analyses are performed. The results show that the oceanic CO2 flux variability peaks when the eastern tropical Pacific has a large sea surface temperature anomaly (SSTA). By contrast, the terrestrial CO2 flux variability peaks when the SSTA appears in the central tropical Pacific. The former pattern of variability resembles the ENSO-mode and the latter the ENSO-modoki1.ConclusionsOur results imply that the oceanic and terrestrial CO2 flux anomalies may correlate either positively or negatively depending on the relative phase of these two modes in the tropical Pacific.

Effects of diagenesis on paleoclimate reconstructions from modern and young fossil corals

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 δ18O records to investigate the effects of submarine and subaerial diagenesis on paleoclimate reconstructions in modern and young sub-fossil corals from the central tropical Pacific. In a 40-year-old modern coral, we find secondary aragonite is associated with relatively high coral δ18O and Sr/Ca, equivalent to sea-surface temperature (SST) artifacts as large as −3 and −5°C, respectively. Secondary aragonite observed in a 350-year-old fossil coral is associated with relatively high δ18O and Sr/Ca, resulting in apparent paleo-SST offsets of up to −2 and −4°C, respectively. Secondary Ion Mass Spectrometry (SIMS) analyses of secondary aragonite yield Sr/Ca ratios ranging from 10.78 to 12.39mmol/mol, significantly higher compared to 9.15±0.37mmol/mol measured in more pristine sections of the same fossil coral. Widespread dissolution and secondary calcite observed in a 750-year-old fossil coral is associated with relatively low δ18O and Sr/Ca. SIMS Sr/Ca measurements of the secondary calcite (1.96–9.74mmol/mol) are significantly lower and more variable than Sr/Ca values from more pristine portions of the same fossil coral (8.22±0.13mmol/mol). Our results indicate that while diagenesis has a much larger impact on Sr/Ca-based paleoclimate reconstructions than δ18O-based reconstructions at our site, SIMS analyses of relatively pristine skeletal elements in an altered coral may provide robust estimates of Sr/Ca which can be used to derive paleo-SSTs.