David A. Mucciarone

A coral‐based reconstruction of Intertropical Convergence Zone variability over Central America since 1707

Seasonal movements of the Intertropical Convergence Zone (ITCZ) control precipitation patterns and cloud cover throughout the tropics. In this study we have reconstructed seasonal and interannual variability of the eastern Pacific ITCZ from 1984 to 1707 using subseasonal δ18O analyses on a massive coral from Secas Island (7°59′N, 82°3′W) in the Gulf of Chiriqui, Panama. The land area that drains into the Gulf of Chiriqui has served to amplify the rainfall effect on nearshore surface waters and coral δ18O composition. During the protracted wet season in Panama, the δ18O of precipitation (δ18Oppt) is reduced on average by 10‰ and sea surface salinity (SSS) along the western coast is reduced up to 11‰. Calibration of the coral δ18O from Secas Island against instrumental sea surface temperature (SST), SSS, precipitation and δ18Oppt data indicate that seasonal rainfall induced variations in seawater δ18O are responsible for ∼80% of the annual δ18O variance. Past El Nino-Southern Oscillation (ENSO) events are recorded as minor 0.2 to 0.4‰ δ18O changes superimposed on the dominant annual δ18Oseawater and salinity variations. The annual cycle in coral δ18O (average 0.9‰) accounts for the largest component of variance at 51% and is the direct result of the annual northward expansion of the eastern Pacific ITCZ. The regularity of the reconstructed seasonal ITCZ cycle indicates that over the length of the record the zone of maximum rainfall in the eastern Pacific has always expanded north to at least Panama in every northern hemisphere summer. Significant interannual and interdecadal δ18O oscillations occur at average periods near 9, 3–7 (ENSO band), 17 and 33 years (listed in order of decreasing variance). Over the past 20 years similar decadal shifts are apparent in coral δ18O from nearshore in the Gulf of Panama. SST data spanning the last 40 years show no decadal changes. This indicates that decadal oscillations in the Gulf of Chiriqui δ18O record are regional features not related to SST changes, but are caused by ITCZ precipitation effects on the δ18O of seawater. A 9-year period in Panama precipitation supports this conclusion and provides a potential link between interannual coral δ18O variations and ITCZ precipitation. It is also shown that the period of the average 9-year interannual period in coral δ18O varies from ∼7.5 years to ∼11.8 years. Variance near 11 years is strongest throughout the 1800s, however, a poor direct correlation with sunspot number and solar irradiance leaves the origin of this interannual oscillation in question. The δ18O time series also contains a long-term trend of −0.40‰ suggesting an increase in precipitation and/or SST since the early 1800s. As the Gulf of Chiriqui coral δ18O time series is the first paleoclimatic record of past variations in the ITCZ, other seasonal-resolution reconstructions of the past behavior of the ITCZ are required to test whether the interannual and long-term variability observed in the eastern Pacific ITCZ is more than regional in scale.

Extreme longevity in proteinaceous deep-sea corals

Deep-sea corals are found on hard substrates on seamounts and continental margins worldwide at depths of 300 to ≈3,000 m. Deep-sea coral communities are hotspots of deep ocean biomass and biodiversity, providing critical habitat for fish and invertebrates. Newly applied radiocarbon age dates from the deep water proteinaceous corals Gerardia sp. and Leiopathes sp. show that radial growth rates are as low as 4 to 35 μm year−1 and that individual colony longevities are on the order of thousands of years. The longest-lived Gerardia sp. and Leiopathes sp. specimens were 2,742 years and 4,265 years, respectively. The management and conservation of deep-sea coral communities is challenged by their commercial harvest for the jewelry trade and damage caused by deep-water fishing practices. In light of their unusual longevity, a better understanding of deep-sea coral ecology and their interrelationships with associated benthic communities is needed to inform coherent international conservation strategies for these important deep-sea habitat-forming species.

Water column sediment fluxes in the Ross Sea, Antarctica: Atmospheric and sea ice forcing

We measured time series of the vertical particle flux at three locations in the Ross Sea, Antarctica, between January 1990 and February 1992 as part of an interdisciplinary project focusing on the accumulation and recycling of organic C and biogenic Si on a polar shelf. We estimate area-wide annual average fluxes through the deep water column of 5 g organic C m−2 yr−l and 30 g biogenic Si m−2 yr−1, values similar to the highest annual average fluxes to the subsurface reported for other areas of the Antarctic continental shelf. Total particle and biogenic Si fluxes are highest during January and February in the southwestern Ross Sea, beneath a seasonally recurrent bloom of the diatom Fragilariopsis curta. Organic C fluxes are highest in the central Ross Sea, consistent with a surface water algal assemblage dominated by the prymnesiophyte Phaeocystis. While organic C flux decreases with depth at all three sites, the result of remineralization within the water column, biogenic opal fluxes are higher in near-bottom traps than at 230 m at the two western Ross Sea sites. Some biogenic opal must be supplied to these deep traps via horizontal advection and possibly resuspension. Fecal pellets and large aggregates contributed between 4 and 70% of the vertical flux and settled at rates of 60 to >400 m d−1. Maximum particle fluxes occur 2 to 10 weeks after surface waters become ice free. We discuss three hypotheses to explain lags between production and settling: (1) advection from surface waters with different ice cover characteristics, (2) lags in the development of a grazing Zooplankton community, and (3) early season windinduced inhibition of primary production. Interannual variability in surface wind stress is empirically linked to variability in biogenic fluxes. Windiness and relative phasing of the annual cycles of ice cover and air temperature may be responsible for the development of different algal communities in the central versus western Ross Sea.

Insolation, Moisture Balance and Climate Change on the South American Altiplano Since the Last Glacial Maximum

Sediment cores from Lake Titicaca contain proxy records of past lake level and hydrologic change on the South American Altiplano. Large downcore shifts in the isotopic composition of organic carbon, C/N, wt.%Corg, %CaCO3, and % biogenicsilica illustrate the dynamic changes in lake level that occurred during the past 20,000 years. The first cores taken from water depths greater than 50 meters in the northern subbasin of the lake are used to develop and extend the paleolake-level record back to the Last Glacial Maximum (LGM). Quantitative estimates of lake level are developed using transfer functions based on the δ 13C of modern lacustrine organic sources and the δ 13C of modern sedimented organic matter from core-tops. Lake level was slightly higher than modern during much of the post-LGM (20,000–13,500 yr BP) and lake water was freshunder the associated outflow conditions. The Pleistocene/Holocene transition (13,500–7,500 yr BP) was a period of gradual regression, punctuated by minor trangressions. Following a brief highstand at about 7250 yr BP, lake level dropped rapidly to 85 m below the modern level, reaching maximum lowstand conditions by 6250 yr BP. Lake level increased rapidly between 5000yr BP and 4000 yr BP, and less rapidly between 4000 yr BP and 1500 yr BP.Lake level remained relatively high throughout the latest Holocene with only minor fluctuations (<12 meters). Orbitally induced changes in solar insolation, coupled with long-term changes in El Niño-Southern Oscillation variability, are the most likely driving forces behind millennial-scale shifts in lake level that reflect regional-scale changes in the moisture balance of the Atlantic-Amazon-Altiplano hydrologic system.

Late Quaternary lake-level changes constrained by radiocarbon and stable isotope studies on sediment cores from Lake Titicaca, South America

We present and compare AMS-14C geochronologies for sediment cores recovered from Lake Titicaca, South America. Radiocarbon dates from three core sites constrain the timing of late Quaternary paleoenvironmental changes in the Central Andes and highlight the site-specific factors that limit the radiocarbon geochronometer. With the exception of mid-Holocene sediments, all cores are generally devoid of macrophyte fragments, thus bulk organic fractions are used to build core chronologies. Comparisons of radiocarbon results for chemically defined fractions (bulk decalcified, humate, humin) suggest that ages derived from all fractions are generally coherent in the post-13,500 yr BP time interval. In the pre-13,500 yr BP time interval, ages derived from humate extracts are significantly younger (300–7000 years) than ages from paired humin residues. Gross age incoherencies between paired humate and humin sub-fractions in pre-13,500 yr BP sediments from all core sites probably reflect the net downward migration of humates. Ages derived from bulk decalcified fractions at our shallow water (90 m) and deep water (230 m) core sites consistently fall between ages derived from humate and humin sub-fractions in the pre-13,500 yr BP interval, reflecting that the bulk decalcified fraction is predominantly a mixture of humate and humin sub-fractions. Bulk decalcified ages from the pre-13,500 yr BP interval at our intermediate depth core site (150 m) are consistently older than humate (youngest) and humin sub-fractions. This uniform, reproducible pattern can be explained by the mobilization of a relatively older organic sub-fraction during and after the re-acidification step following the alkaline treatment of the bulk sediment. The inferred existence of this ‘alkali-mobile, acid-soluble’ sub-fraction implies a different depositional/post-depositional history that is potentially associated with a difference in source material. While internally consistent geochronologies can be developed for the Lake Titicaca sequence using different organic fractions, mobile organic sub-fractions and fractions containing mobile sub-fractions should generally be avoided in geochronology studies. Consequently, we believe humin and/or bulk decalcified ages provide the most consistent chronologies for the post-13,500 yr BP interval, and humin ages provide the most representative ages for sedimentation prior to 13,500 yr BP interval. Using the age model derived from the deep water core site and a previously published isotope-based lake-level reconstruction, we present a qualitative record of lake level in the context of several ice-core records from the western hemisphere. We find the latest Pleistocene lake-level response to changing insolation began during or just prior to the Bolling/Allerod period. Using the isotope-based lake-level reconstruction, we also find the 85-m drop in lake level that occurred during the mid-Holocene was synchronous with an increase in the variability of ice-core δ18O from a nearby icecap, but was not reflected in any of the polar ice-core records recovered from the interior of Antarctica and Greenland.

Long-range atmospheric transport of persistent organic pollutants to remote lacustrine environments

Concentrations, temporal trends and fluxes of persistent organic pollutants (POPs: PAHs, PCBs and PBDEs) were determined in soil and (210)Pb-dated sediment cores from remote lacustrine environments (El Tule and Santa Elena lakes) in rural areas of Central Mexico. In both areas, the concentrations of target analytes in soil and sediment samples were comparable and indicative of slightly contaminated environments. The prevalence of low-molecular-weight PAHs in soils suggested their mainly atmospheric origin, in contrast to the aquatic sediments where runoff contribution was also significant. Increasing contamination trends of PCBs and PBDEs were evident, showing maximum fluxes of 4.8 ± 2.1 and 0.3 ± 0.1 ng cm(-2) a(-1) for PCBs and PBDEs, respectively. The predominance of lower-brominated PBDEs and lower-chlorinated PCBs in soils and sediments indicated that their presence is mostly due to long-range atmospheric transport.

Seasonal radiocarbon and oxygen isotopes in a Galapagos coral: Calibration with climate indices

PUBLICATIONS Geophysical Research Letters RESEARCH LETTER 10.1002/2014GL060504 Key Points: • C and O in seasonal Galapagos corals are inversely correlated • Isotopes are correlated with ENSO and PDO in the east equatorial Pacific • There are two sources of low C waters that upwell at the Galapagos Supporting Information: • Readme • Texts S1–S3 • Figure S1 • Table S1 Correspondence to: E. R. M. Druffel, edruffel@uci.edu Citation: Druffel, E. R. M., S. Griffin, D. S. Glynn, R. B. Dunbar, D. A. Mucciarone, and J. R. Toggweiler (2014), Seasonal radiocarbon and oxygen isotopes in a Galapagos coral: Calibration with climate indices, Geophys. Res. Lett., 41, doi:10.1002/2014GL060504. Received 12 MAY 2014 Accepted 8 JUL 2014 Accepted article online 11 JUL 2014 Seasonal radiocarbon and oxygen isotopes in a Galapagos coral: Calibration with climate indices Ellen R. M. Druffel 1 , Sheila Griffin 1 , Danielle S. Glynn 1 , Robert B. Dunbar 2 , David A. Mucciarone 2 , and J. Robert Toggweiler 3 Department of Earth System Science, University of California, Irvine, California, USA, 2 Environmental Earth System Science, Stanford University, Stanford, California, USA, 3 Geophysical Fluid Dynamics Laboratory/National Oceanic and Atmospheric Administration, Princeton University, Princeton, New Jersey, USA Abstract We present seasonal Δ 14 C and δ 18 O measurements from a Galapagos coral sequence that grew during the early 20th century. Our results show that both Δ 14 C and δ 18 O values are correlated with sea surface temperature in the Nino 3.4 region and are indicators of El Nino–Southern Oscillation. There is a significant inverse correlation between Δ 14 C and δ 18 O values when Δ 14 C is lagged by ~2 months, indicating that sea surface temperature changes precede upwelling changes at this eastern equatorial location. We find that cold season low-Δ 14 C values were higher after the Pacific Decadal Oscillation (PDO) changed from a positive to a negative phase. Cold season high-δ 18 O values were significantly higher after the PDO shift as well. These findings suggest that there are two sources of low-Δ 14 C waters that upwell at the Galapagos, Subantarctic Mode Water and shallow overturning water from the subpolar North Pacific. 1. Introduction Radiocarbon ( 14 C) is naturally produced in the stratosphere and is present in dissolved inorganic carbon (DIC) in seawater. The Δ 14 C (per mil deviation from the 14 C/ 12 C ratio in 19th century wood/atmospheric CO 2 ) values in seawater DIC are highest in the surface and lowest in the deep ocean, because 14 C is radioactive and decays when it is isolated from its source. This decrease of Δ 14 C values with depth makes it a useful tracer of upwelling strength and climate events such as El Nino–Southern Oscillation (ENSO). When upwelling is suppressed during El Nino events, the Δ 14 C values in surface waters and annually banded corals of the east equatorial Pacific (EEP) increase [Brown et al., 1993; Druffel et al., 2007; Guilderson and Schrag, 1998]. An annual Δ 14 C record obtained from a 360 year coral sequence from Urvina Bay, Galapagos Islands, was reported earlier [Druffel et al., 2007]. They attributed interannual and interdecadal variability to changes in ocean circulation, e.g., upwelling strength and the source of upwelled water from the subantarctic convergence zone. Rodgers et al. [2004] showed that Δ 14 C serves as a thermocline proxy in the EEP. The present work focuses on a seasonal Δ 14 C record of a portion of this coral to determine the relationship between Δ 14 C and δ 18 O (primarily recording sea surface temperature in this region) [Dunbar et al., 1994] and major climate shifts, e.g., Pacific Decadal Oscillation (PDO) and ENSO. We report seasonal Δ 14 C values for the period 1939–1954 and seasonal δ 18 O values from 1943 to 1954. We find that Δ 14 C and δ 18 O values are inversely correlated and that Δ 14 C values lag δ 18 O values by ~2 months. We find that cold season low Δ 14 C values shift toward slightly higher values after 1947, coincident with the climate shift of the PDO to a negative phase. 2. Methods The coral used in this study (UR-86) was the same specimen of Pavona clavus that was used in previous studies of annual stable isotope [Dunbar et al., 1994] and radiocarbon [Druffel et al., 2007] measurements over the last 4 centuries. The coral was collected in 1986 from an uplifted reef in Urvina Bay on the west coast of Isabella Island (0°15′S, 91°22′W) in the Galapagos [Dunbar et al., 1994]. The coral section used was pristine aragonite. Our isotopic measurements were performed on seasonal samples that had been drilled at 1 mm spacing (6–13 samples/yr) from the top 15 (Δ 14 C) and 11 (δ 18 O) annual bands with a Dremel tool and diamond bit. DRUFFEL ET AL. ©2014. American Geophysical Union. All Rights Reserved.

A 215-yr coral δ18O time series from Palau records dynamics of the West Pacific Warm Pool following the end of the Little Ice Age

The West Pacific Warm Pool (WPWP) is a critical region of the global climate system that is closely linked with the El Niño-Southern Oscillation (ENSO). We have generated two monthly resolved coral δ18O (δ18OCRL) records from a key region of the WPWP, the Republic of Palau (7′N, 135′E). The isotopic time series span the years 1793–2008 and 1899–2008. During the period of overlap, the two records are well correlated at interannual and annual periods. Multiple lines of evidence demonstrate a strong ENSO signal in Palau δ18OCRL. Our records are consistent with previous investigations of twentieth-century tropical Pacific climate variability. We identify a regionally coherent bi-decadal cycle in the WPWP following the termination of the Little Ice Age. The Palau δ18OCRL records show long-term trends towards warming/freshening, suggesting a century scale increase in the strength of the hydrologic cycle associated with the WPWP. Our study represents an important addition to the network of tropical paleo-archives.

Stable Isotope Record of El Niño-Southern Oscillation Events from Easter Island

Easter Island (also known as Rapa Nui and Isla Pascua) lies within the southeastern Pacific high-pressure system, a feature that along with the Indonesian Low comprises the atmospheric dipole that defines the Southern Oscillation. Sea surface temperatures (SST) in the southeastern Pacific influence this limb of the basin-wide Walker circulation by modulating the stability and magnitude of convection within the regionally descending air. El Nino-Southern Oscillation (ENSO) research has most often focused on variability in the intensity and location of the Indonesian Low convective system or on teleconnections to various parts of the Northern Hemisphere. Long climate records from Easter Island will help elucidate the influence of oceanic variability on the overall ENSO system and its South Pacific teleconnections via the Walker Circulation. In addition, the Easter Island region of the South Pacific Gyre is a source for the shallow subsurface meridional flow that eventually upwells along the equator in the central and eastern Pacific [(Fig. 1); Levitus, 1982; Ji, et al., 1995; Gu and Philander, 1997]. In the northern Pacific, subsurface meridional flow has been suggested as a cause of decade-scale climate anomalies (Gu and Philander, 1997; Zhang et al, 1998). A similar mechanism may operate in the Southern Hemisphere; however, our current lack of a long time series of oceanic climate data from the eastern South Pacific Gyre, limits our ability to study this phenomenon.

Stable Isotope Analyses of Carbonate Complicated by Nitrogen Oxide Contamination: A Delaware Basin Example

ABSTRACT Whole rock subsurface samples from the Cherry Canyon Formation, Delaware Basin, were used to document the presence of a contaminant gas affecting the isotopic composition of acidified carbonate. The whole rock material, when reacted in purified phosphoric acid using the McCrea (1950) method, produces a contaminant mass-46 gas (nitrogen dioxide, NO2). This mass-46 gas contributes to the 18O/16O ratio (mass 46/44), artificially enriching the 18O value and masking the true isotope signature of the CO2 derived from the carbonate minerals. Acidified whole rock samples containing low carbonate (18O (PDB) values, some greater than +30. Conversely, samples with higher carbonate (> 5%) have 18O values ranging from +5 to -8, hence diluting the effects of the contaminant gas on the mass 46/44 ratio. After purifying the CO2 produced by the McCrea (1950) method with a reduction furnace, all of the 18O values fall in the range of 0 to - 12 regardless of carbonate content. Th 16C (PDB) values remain unchanged after reduction furnace purification, indicating no effect on mass 45/44 ratio. The inferred source of the contaminant NO2 gas is from inorganic ammonium adsorbed to interlayer sites of alumina silicates such as illite and mica. This source is supported by the detection of ammonium and clays in the whole rock material and the lack of correlation between percent organic carbon and 18O values influenced by NO2. To eliminate the effect of the contaminant gas on 18O values, we describe a simple procedure that removes the contaminant NO2 gas, yielding the true isotopic signal from the carbonate minerals in whole rock material.