δ13C Decline Research Articles

Tracking palaeotemperatures in Coniacian–Maastrichtian seas

In this study the stable isotopes of belemnites, are presented from the Coniacian–Maastrichtian interval (∼76–66 Ma) derived from the chalks of Yorkshire and Norfolk, UK, deposited on the western North Atlantic shelf. Cathodoluminescence and elemental geochemistry of the belemnites reveals that most of the rostra were well preserved. If interpreted in terms of temperature, our oxygen isotope record reveals that during the Coniacian (at ∼43 °N) the climate was relatively warm, with maximum mean temperatures of ∼26 °C, followed by cooling to <∼21 °C during the Campanian and Maastrichtian. This overall stratigraphic trend is similar to other records, suggesting that the cooling pattern was not a regional trend and, therefore, driven predominantly by global mechanisms. Within our belemnite data, we also observe a decline in δ13C at the Campanian- Maastrichtian boundary, again consistent with other records. This trend has been interpreted as a result of an increased ratio of organic to inorganic carbon introduced into the oceans, driven by increased weathering and reworking of organic-rich sediments exposed on continental shelves during a sea-level fall. The latter related to a build-up of polar ice. Although our oxygen isotope data point to a cooling this was not necessarily linked to polar ice formation.

Forest inventory tree core archive reveals changes in boreal wood traits over seven decades

Boreal forests play an important role in the global carbon (C) cycle, and there is great interest in understanding how they respond to environmental change, including nitrogen (N) and water limitation, which could impact future forest growth and C storage. Utilizing tree cores archived by the Swedish National Forest Inventory, we measured stemwood traits, including stable N and C isotope composition which provides valuable information related to N availability and water stress, respectively, as well as N and C content, and C/N ratio over 1950–2017 in two central Swedish counties covering an area of ca. 55,000 sq. km (n = 1038). We tested the hypothesis that wood traits are changing over time, and that temporal patterns would differ depending on alternative dendrochronological reconstruction methods, i.e. the commonly applied “single tree method” (STM) or a conceptually stronger “multiple tree method” (MTM). Averaged across all MTMs, our data showed that all five wood traits for Picea abies and Pinus sylvestris changed over time. Wood δ15N strongly declined, indicating progressive nitrogen limitation. The decline in δ13C tracked the known atmospheric δ13CO2 signal, suggesting no change in water stress occurred. Additionally, wood N significantly increased, while C and C/N ratios declined over time. Furthermore, wood trait patterns sometimes differed between dendrochronological methods. The most notable difference was for δ15N, where the slope was much shallower for the STM compared to MTMs for both species, indicating that mobility of contemporary N is problematic when using the STM, resulting in substantially less sensitivity to detect historical signals. Our study indicates strong temporal changes in boreal wood traits and also indicates that the field of dendroecology should adopt new methods and archiving practices for studying highly mobile element cycles, such as nitrogen, which are critical for understanding environmental change in high latitude ecosystems.

Enhanced Late Miocene Chemical Weathering and Altered Precipitation Patterns in the Watersheds of the Bay of Bengal Recorded by Detrital Clay Radiogenic Isotopes

AbstractThe late Miocene was a period of declining CO2levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo‐Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition.

The atmospheric bridge communicated the &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C decline during the last deglaciation to the global upper ocean

Abstract. During the early part of the last glacial termination (17.2–15 ka) and coincident with a ∼35 ppm rise in atmospheric CO2, a sharp 0.3‰–0.4‰ decline in atmospheric δ13CO2 occurred, potentially constraining the key processes that account for the early deglacial CO2 rise. A comparable δ13C decline has also been documented in numerous marine proxy records from surface and thermocline-dwelling planktic foraminifera. The δ13C decline recorded in planktic foraminifera has previously been attributed to the release of respired carbon from the deep ocean that was subsequently transported within the upper ocean to sites where the signal was recorded (and then ultimately transferred to the atmosphere). Benthic δ13C records from the global upper ocean, including a new record presented here from the tropical Pacific, also document this distinct early deglacial δ13C decline. Here we present modeling evidence to show that rather than respired carbon from the deep ocean propagating directly to the upper ocean prior to reaching the atmosphere, the carbon would have first upwelled to the surface in the Southern Ocean where it would have entered the atmosphere. In this way the transmission of isotopically light carbon to the global upper ocean was analogous to the ongoing ocean invasion of fossil fuel CO2. The model results suggest that thermocline waters throughout the ocean and 500–2000 m water depths were affected by this atmospheric bridge during the early deglaciation.

Synchronous Marine and Terrestrial Carbon Cycle Perturbation in the High Arctic During the PETM

AbstractThe Paleocene‐Eocene Thermal Maximum (PETM; 56 Ma) is considered to be one of the best analogs for future climate change. The carbon isotope composition (δ13C) of n‐alkanes derived from leaf waxes of terrestrial plants and marine algae can provide important insights into the carbon cycle perturbation during the PETM. Here, we present new organic geochemical data and compound‐specific δ13C data from sediments recovered from an early Cenozoic basin‐margin succession from Spitsbergen. These samples represent one of the most expanded PETM sites and provide new insights into the high Arctic response to the PETM. Our results reveal a synchronous ∼−6.5‰ carbon isotope excursion (CIE) in short‐chain n‐alkanes (nC19; marine algae/bacteria) with a ∼−5‰ CIE in long‐chain n‐alkanes (nC29 and nC31; plant waxes) during the peak of the PETM. Although δ13Cn‐alkanes values were potentially affected via a modest thermal effect (1‰–2‰), the relative changes in the δ13Cn‐alkanes remain robust. A simple carbon cycle modeling suggests peak carbon emission rate could be ∼3 times faster than previously suggested using δ13CTOC records. The CIE magnitude of both δ13C n‐C19 and δ13Cn‐C29 can be explained by the elevated influence of 13C‐depleted respired CO2 in the water column and increased water availability on land, elevated pCO2 in the atmosphere, and changes in vegetation type during the PETM. The synchronous decline in δ13C of both leaf waxes and marine algae/bacteria argues against a significant contribution to the sedimentary organic carbon pool from the weathering delivery of fossil n‐alkanes in the Arctic region.

From Trees to Ecosystems: Spatiotemporal Scaling of Climatic Impacts on Montane Landscapes Using Dendrochronological, Isotopic, and Remotely Sensed Data

AbstractAn interdisciplinary approach is needed for understanding tree physiology and forest biogeochemical cycles undergoing climate change and rising atmospheric CO2. We combined tree ring time series, wood isotope signatures, remotely sensed variables, and climatic data to perform a spatiotemporal scaling analysis of tree physiology and high‐elevation forest responses to rising CO2. The main question addressed is how tree physiological performance of dominant trees can be combined with satellite‐derived information of stand‐level productivity to understand how the landscape shapes the relationship between forest structure and function. Annually resolved tree ring carbon and oxygen isotopic ratios (δ13C and δ18O), carbon isotope discrimination from CO2 to wood (Δ13C), and intrinsic water‐use efficiency (iWUE) of dominant Pinus hartwegii Lindl. trees were sampled and compared against stand‐level normalized difference vegetation index (NDVI) time series from 2000 to 2016. Linear mixed‐effects models tested the effects of elevation, aspect, and time. Carbon and oxygen isotope ratios were correlated with NDVI mainly for the previous fall‐winter season and for the beginning of the growing season. Wood δ13C decreased over time regardless of spatial position, whereas wood δ18O varied as a function of altitude and time. Although Δ13C did not vary with elevation, aspect, or time, a notable decline in Δ13C and peak in iWUE during a severe drought event was evident. Results highlight the link between remotely sensed data, tree ring isotopic composition, and tree physiology as the determining factors to determine spatiotemporal variability in dendroecological studies.

Long-lived coralline alga records multidecadal variability in Labrador Sea carbon isotopes

While the recent decline in the δ13C composition of oceanic dissolved inorganic carbon (DIC) can be attributed to increasing anthropogenic CO2 emissions (13C Suess effect), the causes of natural variability in the δ13C of oceanic DIC (δ13CDIC) are far less understood. Unfortunately, instrumental oceanic DIC measurements are not available prior to the 1970s, prohibiting the observation and study of long-term variability in oceanic carbon isotope dynamics. Thus, in order to identify the main driving forces of changes in oceanic δ13CDIC, multicentury carbon isotope time series that extend from the present into the preindustrial period are required. Such time series may be extracted from the carbonate skeletons of long-lived marine organisms, which have been shown to be robust recorders of fluctuations and trends in oceanic δ13CDIC. In this study, we use an annually-banded coralline alga live-collected from the Labrador shelf to generate a 266-year time series of δ13CDIC changes in the Labrador Sea. Our results indicate that from the 1960s onwards, the rate of δ13CDIC decline in the Labrador Sea slightly exceeds the rate of δ13C decline in the atmosphere, providing support for the enhanced CO2 uptake ability of the Labrador Sea. In addition, the detrended algal δ13C time series displays multidecadal variability with typical Atlantic Multidecadal Oscillation (AMO) frequencies. We show that prior to the late 1980s, algal δ13C compositions significantly correlate with regional sea ice cover (SIC) variability, post-1850 instrumental, reconstructed AMO indices, and solar variability. We speculate that these low-frequency oscillations in δ13C reflect changes in marine primary productivity modulated by a mechanism involving solar changes, the AMO and SIC variability. Our algal carbon isotope time series suggests that while the anthropogenic Suess effect has influenced Labrador Sea δ13CDIC since the 1960s, its influence may have been obscured by the effects of natural climatic variability up until the late 1980s.

Genetic and isotope ratio mass spectrometric evidence for the occurrence of starch degradation and cycling in illuminated Arabidopsis leaves

Although there is a great wealth of data supporting the occurrence of simultaneous synthesis and breakdown of storage carbohydrate in many organisms, previous 13CO2 pulse-chase based studies indicated that starch degradation does not operate in illuminated Arabidopsis leaves. Here we show that leaves of gwd, sex4, bam4, bam1/bam3 and amy3/isa3/lda starch breakdown mutants accumulate higher levels of starch than wild type (WT) leaves when cultured under continuous light (CL) conditions. We also show that leaves of CL grown dpe1 plants impaired in the plastidic disproportionating enzyme accumulate higher levels of maltotriose than WT leaves, the overall data providing evidence for the occurrence of extensive starch degradation in illuminated leaves. Moreover, we show that leaves of CL grown mex1/pglct plants impaired in the chloroplastic maltose and glucose transporters display a severe dwarf phenotype and accumulate high levels of maltose, strongly indicating that the MEX1 and pGlcT transporters are involved in the export of starch breakdown products to the cytosol to support growth during illumination. To investigate whether starch breakdown products can be recycled back to starch during illumination through a mechanism involving ADP-glucose pyrophosphorylase (AGP) we conducted kinetic analyses of the stable isotope carbon composition (δ13C) in starch of leaves of 13CO2 pulsed-chased WT and AGP lacking aps1 plants. Notably, the rate of increase of δ13C in starch of aps1 leaves during the pulse was exceedingly higher than that of WT leaves. Furthermore, δ13C decline in starch of aps1 leaves during the chase was much faster than that of WT leaves, which provides strong evidence for the occurrence of AGP-mediated cycling of starch breakdown products in illuminated Arabidopsis leaves.

Decline in methylmercury in museum-preserved bivalves from San Francisco Bay, California

There are ongoing efforts to manage mercury and nutrient pollution in San Francisco Bay (California, USA), but historical data on biological responses are limited. We used bivalves preserved in formalin or ethanol from museum collections to investigate long-term trends in methylmercury (MeHg) concentrations and carbon and nitrogen isotopic signatures. In the southern reach of the estuary, South Bay, MeHg in the Asian date mussel (Musculista senhousia) significantly declined over the study duration (1970 to 2012). Mean MeHg concentrations were highest (218ng/g dry weight, dw) in 1975 and declined 3.8-fold (to 57ng/g dw) by 2012. This decrease corresponded with closure of the New Almaden Mercury Mines and was consistent with previously observed declines in sediment core mercury concentrations. In contrast, across all sites, MeHg in the overbite clam (Potamocorbula amurensis) increased 1.3-fold from 64ng/g dw before 2000 to 81ng/g dw during the 2000s and was higher than in M. senhousia. Pearson correlation coefficients of the association between MeHg and δ13C or δ15N provided no evidence that food web alterations explained changing MeHg concentrations. However, isotopic composition shifted temporally. South Bay bivalve δ15N increased from 12‰ in the 1970s to 18‰ in 2012. This increase corresponded with increasing nitrogen loadings from wastewater treatment plants until the late 1980s and increasing phytoplankton biomass from the 1990s to 2012. Similarly, a 3‰ decline in δ13C from 2002 to 2012 may represent greater utilization of planktonic food sources. In a complimentary 90day laboratory study to validate use of these preserved specimens, preservation had only minor effects (<0.5‰) on δ13C and δ15N. MeHg increased following preservation but then stabilized. These are the first documented long-term trends in biota MeHg and stable isotopes in this heavily impacted estuary and support the utility of preserved specimens to infer contaminant and biogeochemical trends.

Drought-induced stomatal closure probably cannot explain divergent white spruce growth in the Brooks Range, Alaska, USA.

Increment cores from the boreal forest have long been used to reconstruct past climates. However, in recent years, numerous studies have revealed a deterioration of the correlation between temperature and tree growth that is commonly referred to as divergence. In the Brooks Range of northern Alaska, USA, studies of white spruce (Picea glauca) revealed that trees in the west generally showed positive growth trends, while trees in the central and eastern Brooks Range showed mixed and negative trends during late 20th century warming. The growing season climate of the eastern Brooks Range is thought to be drier than the west. On this basis, divergent tree growth in the eastern Brooks Range has been attributed to drought stress. To investigate the hypothesis that drought-induced stomatal closure can explain divergence in the Brooks Range, we synthesized all of the Brooks Range white spruce data available in the International Tree Ring Data Bank (ITRDB) and collected increment cores from our primary sites in each of four watersheds along a west-to-east gradient near the Arctic treeline. For cores from our sites, we measured ring widths and calculated carbon isotope discrimination (δ13C), intrinsic water-use efficiency (iWUE), and needle intercellular CO2 concentration (C(i)) from δ13C in tree-ring alpha-cellulose. We hypothesized that trees exhibiting divergence would show a corresponding decline in δ13C, a decline in C(i), and a strong increase in iWUE. Consistent with the ITRDB data, trees at our western and central sites generally showed an increase in the strength of the temperature-growth correlation during late 20th century warming, while trees at our eastern site showed strong divergence. Divergent tree growth was not, however, associated with declining δ13C. Meanwhile, estimates of C(i) showed a strong increase at all of our study sites, indicating that more substrate was available for photosynthesis in the early 21st than in the early 20th century. Our results, which are corroborated by measurements of xylem sap flux density, needle gas exchange, and measurements of growth and δ13C along moisture gradients within each watershed, suggest that drought-induced stomatal closure is probably not the cause of 20th century divergence in the Brooks Range.

Microfacies and carbon isotope records of Mississippian carbonates from the isolated Bama Platform of Youjiang Basin, South China: Possible responses to climate-driven upwelling

Changes in Mississippian global paleogeography derived from the reconfiguration of the continents have been suggested to result in a change in oceanic circulation, carbon cycling, as well as in global cooling. Here, integrated δ13Ccarb chemostratigraphy and foraminiferal biostratigraphy across the Mississippian (late Tournaisian, Visean, early Serpukhovian; MFZ6–MFZ16 foraminiferal biozones) of the Gongchuan section located in the isolated Bama Platform in the Youjiang Basin, South China, are presented. The δ13Ccarb trend shows an abrupt decline during late Visean (Asbian-early Brigantian; MFZ13–14). This decline is also observed in subequatorial western Euramerica, whereas coeval sections in subequatorial eastern Euramerica show consistently elevated δ13C values across the entire Visean. The δ13C decline in western Euramerica and the South China Block (eastern Paleo-Tethys) coincides with a global regression with a suggested glacioeustatic origin, the onset of high-frequency climate and sea-level oscillations, and the closure of the Rheic seaway between Euramerica and Gondwana. We propose a model explaining the divergence of δ13C records resulting from the closure of the Rheic seaway and development of upwelling zones in the western margin of Euramerica and the eastern Paleo-Tethys realm. Quantitative microfacies analysis across the Mississippian succession in the Gongchuan section shows facies-independent disappearance of corals and increased proportion of cortoids and filter-feeding organisms at the onset of the Asbian δ13C decline, which may support an increase in nutrient level that can be expected as a result of upwelling.

Exploring climate forcing of growth depression in subfossil South Swedish bog pines using stable isotopes

Comparison between growth variability, based on ring-width (RW) analysis, and moisture-sensitive signals in tree-ring carbon and oxygen stable-isotope composition provides increased understanding of how climate and hydrology influenced bog pines (Pinus sylvestris L.) at two sites in southern Sweden during the mid- and late Holocene. Tree-ring sequences from two subfossil trees collected at raised bogs having different hydrology and catchment size were analyzed to probe the stable-isotope signals associated with two bog-wide episodes of growth depression, one during the Holocene Thermal Maximum and the other during the Neoglacial Transition. The occurrence of lower whole-wood δ13C and cellulose δ13C and δ18O values immediately prior to the onset of growth depression in both trees, suggesting increased atmospheric relative humidity, is consistent with the notion that excessive effective moisture impeded tree growth. Correlation analysis indicates that the growth response lagged about three years behind the decline in δ13C and δ18O values in each tree, possibly reflecting relatively slow rise in the local water table in response to wetter climate.

Changes in Pacific Ocean circulation following the Miocene onset of permanent Antarctic ice cover

We integrate micropaleontological and geochemical records (benthic stable isotopes, neodymium isotopes, benthic foraminiferal abundances and XRF-scanner derived elemental data) from well-dated Pacific Ocean successions (15–12.7Ma) to monitor circulation changes during the middle Miocene transition into a colder climate mode with permanent Antarctic ice cover. Together with previously published records, our results show improvement in deep water ventilation and strengthening of the meridional overturning circulation following major ice expansion at ∼13.9Ma. Neodymium isotope data reveal, however, that the provenance of intermediate and deep water masses did not change markedly between 15 and 12.7Ma. We attribute the increased δ13C gradient between Pacific deep and intermediate water masses between ∼13.6 and 12.7Ma to more vigorous entrainment of Pacific Central Water into the wind-driven ocean circulation due to enhanced production of intermediate and deep waters in the Southern Ocean. Prominent 100kyr ventilation cycles after 13.9Ma reveal that the deep Pacific remained poorly ventilated during warmer intervals at high eccentricity, whereas colder periods (low eccentricity) were characterized by a more vigorous meridional overturning circulation with enhanced carbonate preservation. The long-term δ13C decline in Pacific intermediate and deep water sites between 13.5 and 12.7Ma reflects a global trend, probably related to a re-adjustment response of the global carbon cycle following the last 400kyr carbon maximum (CM6) of the “Monterey Excursion”.

Multiple early Eocene benthic foraminiferal assemblage and δ13C fluctuations at DSDP Site 401 (Bay of Biscay — NE Atlantic)

Abstract Within the last decade, several early Eocene hyperthermals have been detected globally. These transient warming events have mainly been characterized geochemically – using stable isotopes, carbonate content measurements or XRF core scanning – yet detailed micropaleontological records are sparse, limiting our understanding of the driving forces behind hyperthermals and of the contemporaneous paleoceanography. Here, detailed geochemical and quantitative benthic foraminiferal records are presented from lower Eocene pelagic sediments of Deep Sea Drilling Project Site 401 (Bay of Biscay, northeast Atlantic). In calcareous nannofossil zone NP11, several clay-enriched levels correspond to negative δ13C and δ18O bulk-rock excursions with amplitudes of up to ~ 0.75‰, suggesting that significant injections of 12C-enriched greenhouse gasses and small temperature rises took place. Coeval with several of these hyperthermal events, the benthic foraminiferal record reveals increased relative abundances of oligotrophic taxa (e.g. Nuttallides umbonifera) and a reduction in the abundance of buliminid species followed by an increase of opportunistic taxa (e.g. Globocassidulina subglobosa and Gyroidinoides spp.). These short-lived faunal perturbations are thought to be caused by reduced seasonality of productivity resulting in a decreased Corg flux to the seafloor. Moreover, the sedimentological record suggests that an enhanced influx of terrigenous material occurred during these events. Additionally, the most intense δ13C decline (here called level δ) gives rise to a small, yet pronounced long-term shift in the benthic foraminiferal composition at this site, possibly due to the reappraisal of upwelling and the intensification of bottom water currents. These observations imply that environmental changes during (smaller) hyperthermal events are also reflected in the composition of deep-sea benthic communities on both short (

A 200 year temperature record from tree ringδ13C at the Qaidam Basin of the Tibetan Plateau after identifying the optimum method to correct for changing atmospheric CO2andδ13C

[1] Improved understanding of climate influences on tree ring stable carbon isotope (δ13C) ratios for Qilian juniper (Sabina przewalskii Kom.) will improve prospects for long climate reconstructions in northwestern China's Qaidam Basin, where weather stations are widely scattered with relatively short records. Here, we developed an annual-resolution δ13C series from 1800 to 2005 for trees in this extremely arid, high-elevation area. As expected, a significant decline in δ13C (of about 3.5‰) occurred from 1850 to 2005 in response to increasing atmospheric CO2 concentrations and decreasing atmospheric δ13C. High-frequency correlation analysis based on comparison of the tree ring δ13C chronology with recorded weather parameters revealed that mean temperature during the current growing season (April–August) most strongly influenced tree ring δ13C discrimination from 1956 to 2005. To clarify the climatic implications of the long-term trend, we systematically compared four previously published approaches to remove the effects of decreasing atmospheric δ13C from the climate signals. The optimal correction, which accounted for the decline in atmospheric δ13C (δ13Ccor) and for a discrimination rate of about 0.016‰ ppmv−1 for the CO2 partial pressure, captured the strongest temperature signal (r = 0.75, P < 0.001). The historical mean April–August temperatures inferred from the correlations of tree ring δ13C with climate data revealed a persistent warming trend during the past two centuries, especially since the 1980s. Our results therefore reveal a high potential for reconstruction of growing season temperatures on a millennial scale in the northeastern Tibetan Plateau.

A complete high‐resolution Paleocene benthic stable isotope record for the central Pacific (ODP Site 1209)

We have compiled the first stratigraphically continuous high‐resolution benthic foraminiferal stable isotope record for the Paleocene from a single site utilizing cores recovered at Pacific ODP Site 1209. The long‐term trend in the benthic isotope record suggests a close coupling of volcanic CO2 input and deep‐sea warming. Over the short‐term the record is characterized by slow excursions with a pronounced periodic beat related to the short (100 kyr) and long (405 kyr) eccentricity cycle. The phase relationship between the benthic isotope record and eccentricity is similar to patterns documented for the Oligocene and Miocene confirming the role of orbital forcing as the pace maker for paleoclimatic variability on Milankovitch time scales. In addition, the record documents an unusual transient warming of 2°C coeval with a 0.6‰ carbon isotope excursion and a decrease in carbonate content at 61.75 Ma. This event, which bears some resemblance to Eocene hyperthermals, marks the onset of a long‐term decline in δ13C. The timing indicates it might be related to the initiation of volcanism along Greenland margin.

Twentieth century &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;13&amp;lt;/sup&amp;gt;C variability in surface water dissolved inorganic carbon recorded by coralline algae in the northern North Pacific Ocean and the Bering Sea

Abstract. The oxygen isotopic composition and Mg/Ca ratios in the skeletons of long-lived coralline algae record ambient seawater temperature over time. Similarly, the carbon isotopic composition in the skeletons record δ13C values of ambient seawater dissolved inorganic carbon. Here, we measured δ13C in the coralline alga Clathromorphum nereostratum to test the feasibility of reconstructing the intrusion of anthropogenic CO2 into the northern North Pacific Ocean and Bering Sea. The δ13C was measured in the high Mg-calcite skeleton of three C. nereostratum specimens from two islands 500 km apart in the Aleutian archipelago. In the records spanning 1887 to 2003, the average decadal rate of decline in δ13C values increased from 0.03‰ yr−1 in the 1960s to 0.095‰ yr−1 in the 1990s, which was higher than expected due to solely the δ13C-Suess effect. Deeper water in this region exhibits higher concentrations of CO2 and low δ13C values. Transport of deeper water into surface water (i.e., upwelling) increases when the Aleutian Low is intensified. We hypothesized that the acceleration of the δ13C decline may result from increased upwelling from the 1960s to 1990s, which in turn was driven by increased intensity of the Aleutian Low. Detrended δ13C records also varied on 4–7 year and bidecadal timescales supporting an atmospheric teleconnection of tropical climate patterns to the northern North Pacific Ocean and Bering Sea manifested as changes in upwelling.

The 13C Suess effect in scleractinian corals mirror changes in the anthropogenic CO2 inventory of the surface oceans

New δ13C data are presented from 10 coral skeletons collected from Florida and elsewhere in the Caribbean (Dominica, Dominican Republic, Puerto Rico, and Belize). These corals range from 96 to 200 years in age and were collected between 1976 and 2002. The change in the δ13C of the skeletons from these corals between 1900 and 1990 has been compared with 27 other published coral records from the Atlantic, Pacific, and Indian Oceans. The new data presented here make possible, for the first time, a global comparison of rates of change in the δ13C value of coral skeletons. Of these records, 64% show a statistically significant (p &lt; 0.05) decrease in δ13C towards the modern day (23 out of 37). This decrease is attributable to the addition of anthropogenically derived CO2 (13C Suess effect) to the atmosphere. Between 1900 and 1990, the average rate of change of the δ13C in all the coral skeletons living under open oceanic conditions is approximately −0.01‰ yr−1. In the Atlantic Ocean the magnitude of the decrease since 1960,−0.019 yr−1 ±0.015‰, is essentially the same as the decrease in the δ13C of atmospheric CO2 and the δ13C of the oceanic dissolved inorganic carbon (−0.023 to −0.029‰ yr−1), while in the Pacific and Indian Oceans the rate is more variable and significantly reduced (−0.007‰ yr−1 ±0.013). These data strongly support the notion that (i) the δ13C of the atmosphere controls ambient δ13C of the dissolved inorganic carbon which in turn is reflected in the coral skeletons, (ii) the rate of decline in the coral skeletons is higher in oceans with a greater anthropogenic CO2 inventory in the surface oceans, (iii) the rate of δ13C decline is accelerating. Superimposed on these secular variations are controls on the δ13C in the skeleton governed by growth rate, insolation, and local water masses.

Glacial trinity: Neoproterozoic Earth history within the British-Irish Caledonides

Two distinct Neoproterozoic glacial episodes are known for the Dalradian Supergroup in the British-Irish Caledonides, the Port Askaig Formation and the Inishowen–Loch na Cille ice-rafted debris (IRD) beds. Here we describe a third, intermediate between those two, the Stralinchy-Reelan formations, composed of diamictite and IRD. Developed directly above these rocks is the Cranford Limestone, which consists of a basal, 1–6-m-thick, tan-gray dolostone overlain by a variably developed, but as much as 340-m-thick, sequence of thin-bedded limestone and dolostone. This unit exhibits a C isotopic trend that begins negative in the basal dolostone, reaches a nadir of −7‰, and then rises to 0‰–2‰. These characteristics match strikingly those of Marinoan-style cap carbonates. Consequently, we interpret the Port Askaig Formation, the Stralinchy-Reelan units, and the Inishowan–Loch na Cille beds as equivalents of the ca. 700 Ma Sturtian, the 635 Ma Marinoan, and the ca. 580 Ma Gaskiers glacials, respectively. Two additional observations are noteworthy. Carbonate rocks below the Port Askaig Formation record a δ13C decline to −6‰ that implies that such downturns may occur in both pre-Sturtian and pre-Marinoan strata. In addition, the Bonahaven Dolomite is not a cap carbonate to the Port Askaig Formation, but exhibits a δ13C rise to 12‰, which we correlate with the inferred global Keele peak. These data further document the utility of Neoproterozoic glacial–cap carbonate sequences in global correlations and denote the base of the Cranford Linestone as the Cryogenian-Ediacaran boundary.

A distinct δ13C decline in organic lake sediments at the Pleistocene‐Holocene transition in southern Sweden

Values of δ13C obtained from conventional bulk sediment radiocarbon dates encompassing the Pleistocene Holocene boundary have been compiled and plotted against 14C age. In all. 286 lake sediment dates from southern Sweden in the range 8.000 to 13.000 BP have been evaluated. A significant decrease in δ13C values, initiated shortly before 10.000 RP and amounting to 5%, is distinguished. This change is accompanied by increased limnic productivity. decreased erosive input and increased organic carbon content of the sediments. A probable explanation for the δ13C decline in organic material is decreased importance of dissolution of silicates at the transition to the Holocene. During the Late Weichselian. extensive weathering of exposed minerogenic material with subsequent input of bicarbonate to the lake water may have caused a relative enrichment of 13C in dissolved inorganic carbon. Furthermore, the early Holocene increase in terrestrial vegetation cover probably led to an increased supply of 13C depleted carbon dioxide to the lake water by root respiration. Altered limnic vegetation, presumably towards increased production of phytoplankton. could also have contributed to the observed decreasing δ13C trend. The importance of these processes compared to other possible influencing factors. mainly endogenic carbonate production and changes in the global carbon cycle. is discussed.