Μm Yr Research Articles

Variability of hydrographic and biogeochemical properties in the North-western Adriatic coastal waters in relation to river discharge and climate changes

The dynamics of hydrographic and biogeochemical properties in a Northwestern coastal area of the Adriatic Sea were investigated. The time series data from continuous observation (2007–2022) allowed the investigation of annual trends and seasonal cycles along a coastal transect influenced by local river discharge. Various statistical models were used to investigate water temperature, salinity, chlorophyll a, dissolved organic, inorganic and particulate nutrients, precipitation and river discharge. It was found that the local river discharge regime played an essential role in interannual, and seasonal biogeochemical dynamics associated with global climate change in the Mediterranean region. A significant trend towards oligotrophic conditions was detected, as evidenced by the downward trend in the river mouth and on the sea of chlorophyll a (−0.2 μg L−1 in the sea), dissolved organic and inorganic nitrogen and phosphorus (i.e., −0.43 μM yr−1 of DON in the sea and −6.67 of DIN μM yr−1 in the river mouth or −0.07 μM yr−1 of DOP and −0.02 μM yr−1 of DIP in the river mouth) and silicate (−2.47 μM yr−1 in the river mouth) concentrations. Salinity showed a long-term increase in the sea (0.08 yr−1), corresponding to a significant decrease in water discharge from the local river (−0.27 m3 s−1 yr−1) and precipitation (−0.06 mm yr−1). The dissolved organic and inorganic nutrients highlighted a different seasonal accumulation under the river runoff regime. The nutrient enrichment was predominantly driven by river contribution. Data analysis showed that the coastal biogeochemical properties dynamics were mostly influenced by river discharge and precipitation regimes, which in turn are driven by climate change variability in the North-western Adriatic Sea.

Rational design and facile preparation of hybrid superhydrophobic epoxy coatings modified by fluorinated silsesquioxane-based giant molecules via photo-initiated thiol-ene click reaction with potential applications

First, several fluorinated silsesquioxane-based giant molecules (G-SQs) were easily prepared by the photo-initiated thiol-ene click reaction of octa(mercaptopropyl)silsesquioxane (SH8-SQ) with monovinyl(heptatrifluoropropyl)silsesquioxane (CF3-SQ) and perfluorohexyl ethylene with varying stoichiometric ratios. Then, G-SQs were used as low surface energy substances to modify epoxy acrylate resin (EA), which allowed adhesion to different substrates to prepare hydrophobic coatings via photo-initiated thiol-ene click reaction. The hybrid coating can impart stable superhydrophobic properties to cotton fabrics, which possess self-cleaning and oil–water separation function. The cotton fabrics coated by G-SQs-EA can perform oil–water separation very well, whose oil–water separation fluxes and efficiencies are 34,000 L m−2 h−1 and 99 %, respectively. The hybrid hydrophobic coating also provides effective corrosion protection for copper and the corrosion protection effect is further improved by increasing coating thickness. The corrosion current density, corrosion rate and impedance (0.01 Hz) reached 1.17*10−2 μA·cm−2, 0.14 μm yr−1 and 1026 kΩ cm−2, respectively. These excellent results indicate that EA coating modified by G-SQs has potential applications in many fields.

Climatology, trend of aerosol-cloud parameters and their correlation over the Northern Indian Ocean

Aerosols are one of the important atmospheric constituents and exert indirect impact on climate through the modification of microphysical and radiative properties of clouds that in turn perturb the precipitation pattern. Thus, the long term quantification of changes in aerosol and cloud characteristics and their interactions on both temporal as well as spatial scale will provide a crucial information for the better assessment of future climate change. In present study, 18 years (2003–2020) MODerate Resolution Imaging Spectro-radiometer (MODIS) derived aerosol-cloud dataset over the Northern Indian Ocean (NIO) were analysed to assess climatology and trend of aerosol, cloud characteristics and their correlation. We found a strong heterogeneity in spatio-temporal variation of aerosol and cloud parameters over the NIO that are more prominent for the coastal region. The climatological mean of aerosol loading is found high (AOD ≥ 0.5) over the outflow region along the Indian sub-continent and low (AOD ≤ 0.2) over the northern equatorial open ocean. The climatological mean of cloud properties shows dominance of optically thicker deep convective (CTP < 600 hPa and CTT < 260 K) clouds over the southern Bay of Bengal (BoB) and thinner shallow (CTP > 700 hPa and CTT > 273 K) over the northwestern Arabian Sea (AS). Similarly, bigger effective radii (>17 µm) observed along the equatorial open ocean whereas smaller CER (<17 µm) were found over Indian sub-continental coastline and western AS. Further, trend analysis reveals an increasing pattern in AOD (0.002 yr−1), CER (0.051 µm yr−1), LWP (0.033 gm−2 yr−1) and CF (0.002 yr−1) while COD, CTT and CTP show negative trend in order of −0.005 yr−1, −0.094 K yr−1 and −1.160 hPa yr−1, respectively. We also perform similar analysis for seven sub-region of interest (R1 to R7) across the NIO and results show a decreasing pattern in AOD (−0.001 yr−1) at R4 against maximum mean AOD (0.44 ± 0.03). However, coastal sub-regions R1 and R5 illustrate maximum increase in aerosol loading (>0.003 yr−1) suggesting a significant impact of sub-continental outflow over the regions. The spatial correlation of cloud properties with respect to AOD shows a positive slope for CER (0.14) and CF (0.48) and a negative for COD (−0.19), LWP (−0.18), CTT (−0.37), CTP (−0.41). The present study provides in-depth information about the aerosol-cloud characteristics for a long term scale over NIO and could be useful in regional aerosol-cloud interaction induced climate forcing estimation.

Design and preparation of SQ-based superhydrophobic coatings with different substituents for multifunctional applications

Three methoxysilane functionalized cage-like silsesquioxanes (CF3-MSQ, Ph-MSQ and Vi-MSQ) were easily obtained by photo-initiated thiol-ene reaction of mercaptopropyltrimethoxysilane with monovinyl(heptatrifluoropropyl)silsesquioxane (CF3-SQ), monovinyl(heptaphenyl)silsesquioxane (Ph-SQ) and octavinylsilsesquioxane (Vi-SQ), respectively. They were deposited on the surfaces of cotton fabric and Cu sheets via sol-gel chemistry to obtain hydrophobic SQ-coated fabrics and Cu sheets, respectively. The detailed surface features of modified fabrics and Cu sheets were analyzed by FTIR, field emission SEM, XPS and WCA. SQ-based superhydrophobic fabrics with an excellent mechanical stability, chemical stability and photo and thermal stability could show good anti-fouling and self-cleaning abilities.Their omniphobicity to water and oil, SQ-coated fabrics can easily separate oil-water mixtures with efficiencies >99 % at maximum flux values over 96,000 L m−2 h−1. SQ-coated Cu sheets offer excellent corrosion resistance at low corrosion current densities of 3.19*10−2 μA·cm−2, low corrosion rates of 0.37 μm yr−1 with high impedance of 13.3 kΩ cm−2 at 0.01 Hz. Anti-corrosion efficiency was over 99.9 %. The effect of SQ substituents on surface properties and application performances were also investigated. These results indicate modified SQs offer considerable potential in oil-water separation and anti-corrosion, etc.

Machine learning application to layer counting in speleothems

Some speleothems, in particular stalagmites, are laminated at the visible and microscopic scale, with the latter visible using fluorescence microscopy (e.g., confocal laser scanning microscopy). These laminations can be used to supplement speleothem chronologies, although this process is laborious and lateral variations in lamination geometry and quality necessitate a detailed look over an entire scan as opposed to a simple one-dimensional transect. In order to assist this process, we develop a classification-based machine learning algorithm using an open-source machine learning package. This algorithm is optimized for stalagmites growing at 20–100 μm yr−1 and outputs a 2-dimensional layer density map which may aid in quantitatively interpreting past variations in speleothem growth rate. This algorithm requires user supervision and interpretation, as image artefacts and magnification settings may complicate model output.

Cathodic Protection of Complex Carbon Steel Structures in Seawater

Cathodic protection efficiency of complex carbon steel structures in confined seawater environment was studied using a specific experimental device. Schematically, this device consisted of a Plexiglas matrix, crossed by a channel 50 cm long, 5 mm deep, 1.5 to 5 cm wide, which moreover included four bends at 90°. Seawater flowed continuously inside the channel over 12 steel coupons embedded in the Plexiglas matrix. Cathodic protection was applied at a constant potential of −1060 mV vs. Ag/AgCl-seawater with respect to a reference electrode located outside the channel, at the seawater flow entry. The potential of four selected coupons was monitored over time via a microelectrode set close to each coupon. It varied significantly with the distance separating the coupons from the channel entry. At the end of the 3.5-month experiment, a polarization curve was acquired. The residual corrosion rate under cathodic protection was estimated via the extrapolation of the anodic Tafel line. It varied from &lt;1 µm yr−1 to 16 µm yr−1, depending on the potential reached by the coupon (between −900 and −1040 mV vs. Ag/AgCl-seawater) at the end of the experiment and on the properties of the calcareous deposit formed on the steel surface.

Transition metal-based high entropy alloy microfiber electrodes: Corrosion behavior and hydrogen activity

This contribution reveals ultra-high corrosion resistance of high entropy alloys (HEAs), i.e. Ti20Zr20Nb15V15Hf15Ta15 of 1.85 µm yr–1 in alkaline environment, adverting their use for battery/fuel cell components. Formation of several nanometers passive oxide layer confirmed by scanning transmission electron microscopy accounts for corrosion resistance which increases with TiOx content. Cathodic Tafel slope of 67 mV dec–1 and large transfer coefficient of 0.82 obtained for Ti20Zr20Nb20V20Ta20 suggest its use for hydrogen electrocatalysis. High amounts of hydrogen storage, 1.7 wt% in Ti25Zr25Nb15V15Ta20, were confirmed by gas-solid reactions. This HEA also has high corrosion resistance in acidic and saline environments ideal for coatings and surgical tools/implants.

Study of Overprotective-Polarization of Steel Subjected to Cathodic Protection in Unsaturated Soil.

Various electrochemical methods were used to understand the behavior of steel buried in unsaturated artificial soil in the presence of cathodic protection (CP) applied at polarization levels corresponding to correct CP or overprotection. Carbon steel coupons were buried for 90 days, and the steel/electrolyte interface was studied at various exposure times. The coupons remained at open circuit potential (OCP) for the first seven days before CP was applied at potentials of −1.0 and −1.2 V vs. Cu/CuSO4 for the remaining 83 days. Voltammetry revealed that the corrosion rate decreased from ~330 µm yr−1 at OCP to ~7 µm yr−1 for an applied potential of −1.0 V vs. Cu/CuSO4. CP effectiveness increased with time due to the formation of a protective layer on the steel surface. Raman spectroscopy revealed that this layer mainly consisted of magnetite. EIS confirmed the progressive increase of the protective ability of the magnetite-rich layer. At −1.2 V vs. Cu/CuSO4, the residual corrosion rate of steel fluctuated between 8 and 15 µm yr−1. EIS indicated that the protective ability of the magnetite-rich layer deteriorated after day 63. As water reduction proved significant at this potential, it is proposed that the released H2 bubbles damage the protective layer.

Formation of Iron Sulfides on Carbon Steel in a Specific Cement Grout Designed for Radioactive Waste Repository and Associated Corrosion Mechanisms.

Carbon steel coupons were buried in a specific low-pH cement grout designed for radioactive waste disposal and left 6 months in anoxic conditions at 80 °C. The corrosion product layers were analyzed by µ-Raman spectroscopy, XRD, and SEM. They proved to be mainly composed of iron sulfides, with magnetite as a minor phase, mixed with components of the grout. Average corrosion rates were estimated by weight loss measurements between 3 and 6 µm yr−1. Corrosion profiles revealed local degradations with a depth up to 10 µm. It is assumed that the heterogeneity of the corrosion product layer, mainly composed of conductive compounds (FeS, Fe3S4, and Fe3O4), promotes the persistence of corrosion cells that may lead to locally aggravated degradations of the metal. New cement grouts, characterized by a slightly higher pH and a lower sulfide concentration, should then be designed for the considered application.

Compatibility of container materials for Concentrated Solar Power with a solar salt and alumina based nanofluid: A study under dynamic conditions

Thermal energy storage (TES) is an efficient solution for improving the dispatchability of Concentrated Solar Power (CSP) plants. A system, consisting of two tanks with Solar Salt (NaNO3 60% wt. and KNO3 40% wt.) is commonly used. However, the investment cost of this technology is very high, due to the huge amount of salts required (thousands of tons). A pronounced interest is evident for improving the thermophysical properties of molten salts by adding small amounts of nanoparticles in order to reduce the mass of molten salts at CSP. At the moment, the effect of nanoparticle addition on corrosion of container materials is poorly explored. In particular, there are no works regarding the dynamic effect of nanoparticles on the corrosivity of molten salts. In this work we present first ever dynamic corrosion tests for Solar salt doped with alumina nanoparticles (1% wt.). Carbon Steel A516 and SS347, used in double-tank system, were tested. Corrosion rates were 94.8 μm yr−1 and negligible respectively (1000 h, 385 °C). Detailed examination of construction materials revealed incorporation of nanoparticles into the corrosion layer and considerably lower corrosion rate as compared to the previously reported work on the nanoparticles-free Solar salt.

The predominance of post‐wildfire erosion in the long‐term denudation of the Valles Caldera, New Mexico

AbstractWildfires can dramatically increase erosion rates over time scales on the order of several years, yet few data firmly constrain the relative importance of post‐wildfire erosion in the long‐term denudation of landscapes. We tested the hypothesis that wildfire‐affected erosion is responsible for a large majority of long‐term denudation in the uplands of the Valles Caldera, New Mexico, by quantifying erosion rates in wildfire‐affected and non‐wildfire‐affected watersheds over short (~100–101 years) time scales using suspended sediment loads, multitemporal terrestrial laser scanning, and airborne laser scanning and over long (~103–106 years) time scales using 10Be inventories and incision into a dated paleosurface. We found that following the Las Conchas fire in 2011, mean watershed‐averaged erosion rates were more than 1000 µm yr−1, i.e., ~103–105 times higher than nearby unburned watersheds of similar area, relief, and lithology. Long‐term denudation rates are on the order of 10–100 µm yr−1. Combining data for wildfire‐affected and non‐wildfire‐affected erosion rates into a long‐term denudation rate budget, we found that wildfire‐affected erosion is responsible for at least 90% of denudation over geologic time scales in our study area despite the fact that such conditions occur only at a small fraction of the time. Monte Carlo analyses demonstrate that this conclusion is robust with respect to uncertainties in the rates and time scales used in the calculations.

Spatial and temporal trends in summertime climate and water quality indicators in the coastal embayments of Buzzards Bay, Massachusetts

Abstract. Degradation of coastal ecosystems by eutrophication is largely defined by nitrogen loading from land via surface water and groundwater flows. However, indicators of water quality are highly variable due to a myriad of other drivers, including temperature and precipitation. To evaluate these drivers, we examined spatial and temporal trends in a 22-year record of summer water quality data from 122 stations in 17 embayments within Buzzards Bay, MA (USA), collected through a citizen science monitoring program managed by Buzzards Bay Coalition. To identify spatial patterns across Buzzards Bay's embayments, we used a principle component and factor analysis and found that rotated factor loadings indicated little correlation between inorganic nutrients and organic matter or chlorophyll a (Chl a) concentration. Factor scores showed that embayment geomorphology in addition to nutrient loading was a strong driver of water quality, where embayments with surface water inputs showed larger biological impacts than embayments dominated by groundwater influx. A linear regression analysis of annual summertime water quality indicators over time revealed that from 1992 to 2013, most embayments (15 of 17) exhibited an increase in temperature (mean rate of 0.082 ± 0.025 (SD) °C yr−1) and Chl a (mean rate of 0.0171 ± 0.0088 log10 (Chl a; mg m−3) yr−1, equivalent to a 4.0 % increase per year). However, only seven embayments exhibited an increase in total nitrogen (TN) concentration (mean rate 0.32 ± 0.47 (SD) µM yr−1). Average summertime log10(TN) and log10(Chl a) were correlated with an indication that the yield of Chl a per unit total nitrogen increased with time suggesting the estuarine response to TN may have changed because of other stressors such as warming, altered precipitation patterns, or changing light levels. These findings affirm that nitrogen loading and physical aspects of embayments are essential in explaining the observed ecosystem response. However, climate-related stressors may also need to be considered by managers because increased temperature and precipitation may worsen water quality and partially offset benefits achieved by reducing nitrogen loading.

Long-term alkalinity decrease and acidification of estuaries in northwestern Gulf of Mexico.

More than four decades of alkalinity and pH data (late 1960s to 2010) from coastal bays along the northwestern Gulf of Mexico were analyzed for temporal changes across a climatic gradient of decreasing rainfall and freshwater inflow, from northeast to southwest. The majority (16 out of 27) of these bays (including coastal waters) showed a long-term reduction in alkalinity at a rate of 3.0-21.6 μM yr(-1). Twenty-two bays exhibited pH decreases at a rate of 0.0014-0.0180 yr(-1). In contrast, a northernmost coastal bay exhibited increases in both alkalinity and pH. Overall, the two rates showed a significant positive correlation, indicating that most of these bays, especially those at lower latitudes, have been experiencing long-term acidification. The observed alkalinity decrease may be caused by reduced riverine alkalinity export, a result of precipitation decline under drought conditions, and freshwater diversion for human consumption, as well as calcification in these bays. A decrease in alkalinity inventory and accompanying acidification may have negative impacts on shellfish production in these waters. In addition, subsequent reduction in alkalinity export from these bays to the adjacent coastal ocean may also decrease the buffer capacity of the latter against future acidification.

Variability in growth rates of long-lived black coral Leiopathes sp. from the Azores

Five colonies of black coral Leiopathes sp. were collected as bycatch from depths of 293 to 366 m from the Condor, Acor, and Voador seamounts (Azores region). The colonies had axial diameters between 4.9 and 33.1 mm and heights between 43 and 175 cm. Their ages and radial growth rates were estimated using radiocarbon dating. Results indicated that the smallest and largest colonies had similar radial growth rates of 5 to 7 µm yr �1 , whereas the other 3 colonies had grown more rapidly by a factor of 3 to 5 at ~20 to 30 µm yr �1 . Colony lifespan ranged between 265 ± 90 and 2320 ± 90 yr. Fine-scale sampling along a radial transect from the edge to the center of the 2320 yr old Leiopathes sp. revealed variable growth rates throughout the colony lifespan. Slower radial growth rates of ~4 to 5 µm yr �1 were recorded over the initial 1600 yr and the last 300 yr of its life span, and a period of more rapid growth (20 µm yr �1 ) over the intermediate 400 yr of its life. Variability in radial growth rates among colonies resulted in colony ages that were not linearly correlated to colony axis diameter or height. Our findings of great longevity and slow growth rates for Leiopathes sp. agree with other Leiopathes sp. age and growth studies, indicating that colony and population recovery from damage or removal may take centuries to millennia.

Waste container durability: monitoring of a stainless steel 4 metre box over 12 years

AbstractIn the UK, most intermediate level radioactive waste is packaged in stainless steel containers. It is important that containers should maintain their integrity for extended periods of storage prior to final disposal. A prototype 4 metre box fabricated from 304S11 stainless steel was monitored at an inland rural building for over twelve years to gain experience in monitoring environmental conditions and corrosion during storage. A wide range of different types of aerosol particles were observed on the surfaces and in the air. They contained corrosive ions such as chloride, as well as other anions such as sulfate and nitrate. The chloride deposition rate was between 0.1 and 4 μg cm−2 yr−1 depending on the orientation and location of the surface, with a chloride/sulfate ratio ranging from ∼0.3–2. The temperature and relative humidity typically ranged from 0–30°C and 40–90%, respectively. The greatest degree of corrosion developed on the base of the box, which had elevated chloride concentrations (10–140 μg cm−2). However, there was little evidence of corrosion propagation on the surface of the box and no evidence of stress corrosion cracking. The average pit propagation rates on a 316L coupon mounted next to the 4 m box were &lt;1 μm yr−1.

Nutrients and particulate organic matter discharged by the Changjiang (Yangtze River): Seasonal variations and temporal trends

From September 2009 to August 2010, intensive monthly sampling of nutrients was conducted at two stations at the mouth of the Changjiang (Yangtze River). Particulate organic carbon (POC), particulate nitrogen (PN), and their stable isotope values (δ13C and δ15N) were also measured in selected samples of all months. Most nutrients (nitrate, phosphate, ammonia, and nitrite) as well as POC, PN, and δ13C displayed peak values when the highest or lowest Changjiang monthly discharges occurred, suggesting the Changjiang discharges strongly influence the seasonal variations of these chemicals. The sharply increases in concentrations of ammonia and nitrite in winter probably suggest nitrification was greatly depressed during this cold period. Using five interpolation methods, the annual discharge fluxes of nutrients, POC, and PN from the Changjiang to the East China Sea shelf were calculated. Combining this nutrient data with data from previous studies, the seasonal Mann‐Kendall test, in which the influence of seasonal variation was considered, suggests concentrations of nitrate and phosphate in the Changjiang have significantly increased during recent decades at rates of 2.2μM yr−1 and 0.03 μM yr−1, respectively; no significant trend for silicate was noted. Decreased POC annual fluxes along with sharply decreased suspended particulate matter yields were also seen in recent years (1993–2010). However, no distinct changes of δ13C, δ15N, and the POC/PN ratio, which describe the particulate organic matter properties, were observed during this period.

Growth rate and age distribution of deep-sea black corals in the Gulf of Mexico

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 423:101-115 (2011) - DOI: https://doi.org/10.3354/meps08953 Growth rate and age distribution of deep-sea black corals in the Gulf of Mexico N. G. Prouty1,*, E. B. Roark2, N. A. Buster3, S. W. Ross4 1US Geological Survey, 400 Natural Bridges Drive, Santa Cruz, California 95060, USA 2Department of Geography, Texas A&M University, College Station, Texas 77843, USA 3US Geological Survey, 600 Fourth Street South, St Petersburg, Florida 33701, USA 4University of North Carolina at Wilmington, Center for Marine Science, 5600 Marvin Moss Ln, Wilmington, North Carolina 28409, USA *Email: nprouty@usgs.gov ABSTRACT: Black corals (order Antipatharia) are important long-lived, habitat-forming, sessile, benthic suspension feeders that are found in all oceans and are usually found in water depths greater than 30 m. Deep-water black corals are some of the slowest-growing, longest-lived deep-sea corals known. Previous age dating of a limited number of black coral samples in the Gulf of Mexico focused on extrapolated ages and growth rates based on skeletal 210Pb dating. Our results greatly expand the age and growth rate data of black corals from the Gulf of Mexico. Radiocarbon analysis of the oldest Leiopathes sp. specimen from the upper De Soto Slope at 300 m water depth indicates that these animals have been growing continuously for at least the last 2 millennia, with growth rates ranging from 8 to 22 µm yr–1. Visual growth ring counts based on scanning electron microscopy images were in good agreement with the 14C-derived ages, suggestive of annual ring formation. The presence of bomb-derived 14C in the outermost samples confirms sinking particulate organic matter as the dominant carbon source and suggests a link between the deep-sea and surface ocean. There was a high degree of reproducibility found between multiple discs cut from the base of each specimen, as well as within duplicate subsamples. Robust 14C-derived chronologies and known surface ocean 14C reservoir age constraints in the Gulf of Mexico provided reliable calendar ages with future application to the development of proxy records. KEY WORDS: Black corals · Radiocarbon age · Growth rates · Gulf of Mexico · Oil spill Full text in pdf format Supplementary material PreviousNextCite this article as: Prouty NG, Roark EB, Buster NA, Ross SW (2011) Growth rate and age distribution of deep-sea black corals in the Gulf of Mexico. Mar Ecol Prog Ser 423:101-115. https://doi.org/10.3354/meps08953 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 423. Online publication date: February 10, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Recent loss of floating ice and the consequent sea level contribution

We combine new and published satellite observations and the results of a coupled ice‐ocean model to provide the first estimate of changes in the quantity of ice floating in the global oceans and the consequent sea level contribution. Rapid losses of Arctic sea ice and small Antarctic ice shelves are partially offset by thickening of Antarctic sea ice and large Antarctic ice shelves. Altogether, 746 ± 127 km3 yr−1 of floating ice was lost between 1994 and 2004, a value that exceeds considerably the reduction in grounded ice over the same period. Although the losses are equivalent to a small (49 ± 8 μm yr−1) rise in mean sea level, there may be large regional variations in the degree of ocean freshening and mixing. Ice shelves at the Antarctic Peninsula and in the Amundsen Sea, for example, have lost 481 ± 38 km3 yr−1.

Multi-century time-series of 15N and 14C in bamboo corals from deep Tasmanian seamounts: evidence for stable oceanographic conditions

Bamboo corals (Family Isididae) are an important component of seamount benthos south of Tasmania. Besides having lifespans of up to 400 yr, little is known about their basic ecology, nor how to decode potential climate signals encoded in their skeletons. We explored the stable nitrogen isotope and radiocarbon compositions of the skeletal organic fraction of the genera Isidella, Keratoisis and Lepidisis collected from 3 Tasmanian seamounts. Analyses were performed on tissues and organic node growth rings sampled at a temporal resolution of 1 to 4 yr. Radiocarbon chronologies exhibited nuclear bomb signals characteristic of surface waters and constrained radial growth rates to ~35 ± 10 µm yr–1 for 3 specimens of the genus Lepidisis and 113 ± 17 µm yr–1 for 1 specimen of Isidella. δ15N values of the living tissue and underlying gorgonin were similar and averaged 9 to 12‰. Records of δ15N from 8 different specimens showed subtle, quasi-decadal patterns over the last ~100 yr, although the amplitude of these features (~1‰) was similar to the average intra- and intercolony reproducibility. These results demonstrate the utility of deep-sea corals to track seamount biogeochemical processes over long time scales, and suggest that the extent of nutrient depletion of surface waters and associated trophic dynamics have remained relatively constant in this region over centuries. This provides an important baseline for the evaluation of the impacts of anthropogenic climate change.

Growth validation of gold coral Gerardia sp. in the Hawaiian Archipelago

Colonies of the Hawaiian gold coral Gerardia sp. (n = 48) were measured, marked and then revisited 1 to 9 yr later to look for evidence of linear growth. The video images showed no change in the proportional size of the coral colonies relative to the marker pots left on the bottom and no change in the pattern of distal branches. Few of the measured delta values exceeded the error of our measurement technique, and the detected change in the sample was statistically indistinguish- able from zero. Even though the temperature cycle in the coral beds appears seasonal, these obser- vations indicate that gold coral growth is much slower than growth estimates derived from basal stem ring counts treated as annuli. The period of study was too short to effectively evaluate the validity of life span estimates from radiocarbon studies. The variability in radiocarbon data was assessed with broad sampling (n = 23) across study sites to reveal a mean life span of 950 yr with an overall radial growth of ~41 µm yr -1 . Based on the calculation of a gross radiocarbon linear growth rate of 2.2 ± 0.2 mm yr -1 , the sample colonies marked in the field would have grown ~1.8 cm during the study period.