High-resolution Stable Isotope Analysis Research Articles

Contrasting life-history responses to climate variability in eastern and western North Pacific sardine populations

Massive populations of sardines inhabit both the western and eastern boundaries of the world’s subtropical ocean basins, supporting both commercial fisheries and populations of marine predators. Sardine populations in western and eastern boundary current systems have responded oppositely to decadal scale anomalies in ocean temperature, but the mechanism for differing variability has remained unclear. Here, based on otolith microstructure and high-resolution stable isotope analyses, we show that habitat temperature, early life growth rates, energy expenditure, metabolically optimal temperature, and, most importantly, the relationship between growth rate and temperature are remarkably different between the two subpopulations in the western and eastern North Pacific. Varying metabolic responses to environmental changes partly explain the contrasting growth responses. Consistent differences in the life-history traits are observed between subpopulations in the western and eastern boundary current systems around South Africa. These growth and survival characteristics can facilitate the contrasting responses of sardine populations to climate change.

First steps in reconstructing Early Jurassic sea water temperatures in the Andean Basin of northern Chile based on stable isotope analyses of oyster and brachiopod shells

The stable isotope (δ13C, δ18O) composition of a collection of Lower Jurassic brachiopods and oysters from the Andean Basin of northern Chile was analyzed. The results allow the first reconstruction of absolute water temperatures for several ammonite zones in the Lower Jurassic of South America. The temperature record starts with comparatively high values in the Late Sinemurian (average: 27.0 °C; Raricostatum Zone). Just before the Sinemurian–Pliensbachian transition, temperatures dropped to an average of 24.3 °C. The lowest temperature value in the dataset was recorded for a brachiopod shell of the latest Pliensbachian Spinatum Zone (19.6 °C). No data are available for the Early Toarcian, but results for the late Toarcian show again comparatively warm conditions (average: 24.4 °C; Thouarsense–Levesquei zones). Even though more material and analyses are necessary to corroborate the recorded temperatures, the present dataset seems to indicate the global nature of the Late Pliensbachian Cooling Event. In contrast, the global warming during the Toarcian Oceanic Anoxic Event has not been recorded due to a lack of Early Toarcian material. The δ13C record of brachiopods and oysters documents a gradual increase in values representing background conditions. Oyster shells were used for high-resolution stable isotope analyses and show seasonal temperature fluctuations over a period of around 3 years in the life time of the bivalves. If explained only by temperatures, the δ18O values point to a minimum estimate for the seasonality in the late Toarcian of slightly more than 3 °C.

Periodicity in stromatolitic lamination: A potential record of ENSO, NAO, and SUNSPOT in the Miocene lacustrine record of the Ebro Basin, Spain

The spectral decomposition of time series obtained from ancient rock records can be used to study the similarity between the dynamics of present-day and past climate systems. A high-resolution periodicity analysis of luminance and lamina thickness of lacustrine stromatolites in the Ebro Basin (northeast of Iberian Peninsula) reveals a significant signal of interannual and decadal climatic variability in the Miocene. This is one out of very few works that presents the use of spectral analysis to estimate the potential of stromatolite lamination as multiple-scale recorders of climate parameters. The effects of precipitation and evaporation variations on stromatolite lamination have been detected at three orders of cyclicity based on textural and high-resolution stable-isotope analyses (C and O) obtained in prior studies. These analyses also revealed that the light and dark simple lamina couplets are identified with annual cycles (third-order isotopic cycles). In the present study, the spectral analysis results obtained through different paths in five stromatolite specimens reveal significant periods in the power spectrum at around 2.5, 3.7, 5, 7, 10, and 22 years. These cycles can be correlated with the typical oscillation bands of different climate-related agents. The 2.5-year period corresponds to the Quasi Biennial Oscillation (QBO), or to the biennial component of the El Niño-Southern Oscillation (ENSO), or to the North Atlantic Oscillation (NAO). The 3 to 5 and 5 to 7-year bands can be linked to ENSO or NAO variability (second-order isotopic cycles). The 8 to 11-year bands fit the 11-year Schwabe (first-order isotopic cycles) and 22 to 23-year fit the 22-year Hale sunspot cycles. Thus, the stromatolite growth was controlled by ENSO, NAO, and solar activity cycles. The close relationship between these climate-related agents makes it difficult to specify the dominant agent controlling the stromatolite growth. Nevertheless, the significant periods obtained from this study, within interannual (2.5, 3.7, 5, 7 years), decadal (10, 22 years), and even multidecadal bands (37–42 years), support the existence, and concurrence, of ENSO and NAO precursors during the early and middle Miocene.

The Middle to Upper Jurassic stable isotope record of Madagascar: Linking temperature changes with plate tectonics during the break-up of Gondwana

Stable isotope (δ18O, δ13C) analyses were performed on well preserved belemnites, oysters, and rhynchonellid brachiopods from the Middle to Upper Jurassic of the Morondava Basin in southern Madagascar. Both brachiopods and oysters indicate similar average temperatures of 18.7 to 19.3 °C in the Early Callovian, followed by a temperature decrease towards the Middle Oxfordian (13.9 °C) and a minimum in the Early Kimmeridgian (12.3 °C). In contrast, belemnites from the Oxfordian show lower average temperatures of 10.0 °C, which is likely caused by specific conditions for these organisms (e.g., different fractionation or life habits). Additionally, three oysters from the Upper Oxfordian and Lower Kimmeridgian were used for high-resolution stable isotope analyses. The data show seasonal fluctuations of >6 °C around averages between 14.4 and 14.7 °C. Latitudinal temperature gradients for the Callovian and Kimmeridgian are similar to today at the examined low latitudes of the southern hemisphere. The observed cooling of around 5 °C from the Callovian to the Oxfordian/Kimmeridgian can be attributed to a concurrent southward drift of Madagascar during the break-up of Gondwana. Thus, the study underlines the importance of considering palaeogeography in interpreting stable isotope data as well as the potential of detecting and timing palaeogeographic events by using stable isotope analyses.

High-resolution chemostratigraphy of a Miocene wedge-top carbonate shelf (San Marino Fm., Northern Apennines, Italy): The major role of the Monterey global fertility event

The evolution of the San Marino carbonate succession, developed on a wedge-top basin of the northern Apennines during the Middle Miocene (Torriana outcrop, Marecchia Valley), was studied through a high-resolution stable isotope analysis on different carbonate components. A marked positive carbon isotopic excursion is identified at ca. 16 Ma. The excellent correlation of the San Marino δ13C carbonates with the global δ13C reference curve from Zachos et al. (2008) allows to link the marked positive δ13C present in the San Marino section with the global carbon isotope maximum of the Monterey event. Subordinate long-eccentricity-driven δ13C cycles (~405 kyr) as recorded by Holbourn et al. (2007) were also identified. The correlation with carbon signatures of coeval successions of the Mediterranean region shows that this main carbon isotopic excursion at the Burdigalian–Langhian boundary is widely recorded and predates the crisis of these heterozoan shelves. The demise of the San Marino shelf resulted from a combination of global and regional factors that controlled the nutrient budget, the detrital input and the subsidence of the basin. The high-resolution chemostratigraphy of San Marino succession shows that even though the shelf evolved in the complex setting of a wedge-top basin, which should be largely influenced by local factors (i.e. tectonic subsidence and detrital input), it records the Monterey event and its eccentricity paced rhythms with high precision. This highlights the strong connection of the Monterey event with the development and subsequent demise of shallow water carbonate depositional systems in the Mediterranean, irrespective of variable and changing local conditions.

Middle to Late Jurassic equatorial seawater temperatures and latitudinal temperature gradients based on stable isotopes of brachiopods and oysters from Gebel Maghara, Egypt

Stable isotope (δ18O, δ13C) analyses of brachiopod and oyster shells from the Gebel Maghara, Egypt, were used to reconstruct the first detailed dataset on peri-equatorial water temperatures during the Middle to Late Jurassic. Throughout this time interval, temperatures remained relatively constant around an average of 25.7°C. Slightly warmer conditions existed in the Early Bathonian (~27.0°C), while the Kimmeridgian shows the lowest temperatures (~24.3°C). As expected for a tropical palaeolatitude, the seasonality was very low (<2°C) as reconstructed by high-resolution stable isotope analyses of two oyster shells. Latitudinal temperature gradients in the Middle Jurassic were much steeper than previously expected and comparable to today. During the Kimmeridgian (Late Jurassic), temperatures in Europe were generally warmer leading to weaker latitudinal gradients. On average, water temperatures reconstructed from stable isotopes for Jurassic localities above the thermocline are lower than Recent sea-surface temperatures (based on currently used estimates for the δ18O value of seawater).

Seasonality in sea surface temperatures from δ18O inCladocora caespitosa: modern Adriatic to late Pleistocene, Gulf of Corinth

High-resolution stable isotope analysis of coral skeletons is an established method to help reconstruct seawater growth temperatures for palaeoenvironmental reconstructions. Here we investigated the temperate, colonial, Mediterranean scleractinian coral Cladocora caespitosa. We first studied modern Adriatic corals from Mljet (Croatia) where growth temperatures were known. A clear sinusoidal cyclicity is present in the d18O of the modern coral skeletons with average cycle minima 3.3‰ and average maxima 1.6‰. Cyclicity approximately matches the number of seasonal growth band pairs in each sample, implying a genetic link between d18O cyclicity and factors that determine seasonal growth band development, here mainly water temperature. A derived and calibrated species-specific d18O–temperature relationship was then used to reconstruct growth temperatures from fossil C. caespitosa. This was applied to well-preserved material collected from late Pleistocene deposits (MIS 1, 5 and 7) around the Gulf of Corinth, Greece. Clear seasonal d18O signals are seen in all the fossil samples. MIS 5e was the warmest period studied with a lower than modern seasonal temperature range. The Early to mid-Holocene probably experienced the lowest temperatures while conditions in MIS 7a/c were probably the wettest with most freshwater input into the Gulf.

Seasonality in low latitudes during the Oxfordian (Late Jurassic) reconstructed via high-resolution stable isotope analysis of the oyster Actinostreon marshi (J. Sowerby, 1814) from the Kachchh Basin, western India

A high-resolution stable isotope (δ18O, δ13C) analysis of a specimen of the oyster Actinostreon marshi (J. Sowerby, 1814) from the Lower Oxfordian of the Kachchh Basin in western India was used to reconstruct average seasonal temperatures over a consecutive time interval of 10 years. The recorded temperatures during this period varied around a mean of 13 °C (maximum: 15.1 °C; minimum: 11.4 °C) with a generally low seasonality between 1 and 3 °C. Such weak seasonal changes can be expected from a subtropical palaeolatitude between 25° and 30°S. However, the low average temperatures are in contrast to studies on broadly contemporaneous fossils from Europe and the southern Malagasy Gulf which point to much warmer conditions in these areas. It is therefore proposed that the low temperatures in the Kachchh Basin are caused by upwelling currents which influenced the north-western coast of India during the Late Jurassic.

Planktonic foraminiferal biostratigraphy and mechanisms in the extinction of Morozovella in the late middle Eocene

The muricate planktonic foraminiferal genera Morozovella and Acarinina were abundant and diverse during the upper Palaeocene to middle Eocene and dominated the tropical and subtropical assemblages. A significant biotic turnover in planktonic foraminifera occurred in the latest middle Eocene with a notable reduction in the acarininid lineage and the extinction of the morozovellids. These genera are extensively employed as palaeoclimatic and biostratigraphic markers and, therefore, this turnover episode is an important event in the record of the Cenozoic planktonic foraminifera. Sediments from the western North Atlantic (Ocean Drilling Program Site 1052) were examined in order to investigate these extinction events, in terms of both timing and mechanisms. Biostratigraphic events of the middle and late Eocene have been examined with a sampling resolution of approximately 3 kyr. These have been calibrated to the magneto- and astrochronology to accurately define the timing of key biostratigraphic events, particularly the extinction of Morozovella spinulosa which is a distinct biomarker for late middle Eocene sediments. High-resolution biostratigraphy reveals that the extinctions in the muricate group occurred in a stepwise form. The large acarininids ( Acarinina praetopilensis) terminate 10 kyr prior to the extinction of M. spinulosa and small acarininids ( Acarinina medizzai and Acarinina echinata) continue into the upper Eocene. High-resolution stable isotope analyses have been conducted on planktonic and benthic foraminifera from the western North Atlantic to reconstruct sea surface temperatures (SSTs) and deep water temperatures and the structure of the water column around this major biotic turnover. Whilst the extinctions of M. spinulosa and A. praetopilensis occur during a long-term cooling trend, the biotic turnover in the muricate group does not appear to be related to significant climatic change. Sea surface temperatures decrease slowly prior to the extinction events, and there is no evidence for a large-temperature shift associated with the faunal changes. The turnover event was therefore probably related to the increased surface water productivity and the deterioration of photosymbiotic partnerships with algae.

High resolution stable isotope analysis of a Tasmanian speleothem

High resolution oxygen and carbon isotope analyses of part of a uniform diameter stalagmite from a cave in northern Tasmania have been used to study the climatic transition from stadial to interstadial conditions during the early Last Glacial (109-95 ka). A significant change in oxygen isotope values suggests that temperature warmed rapidly by approximately 2°-3°C between 100 and 97 ka. A decrease in carbon isotope values berween I 0 I and 98 ka indicates that moisture availability was increasing slightly in advance of rising temperature.

High-resolution stable isotope analysis of tree rings: implications of 'microdendroclimatology' for palaeoenvironmental research

High-resolution stable isotope analyses were carried out on a sample of oak (Quercus petraea) from Cultra, Co Down, UK. A sampling strategy of unparallelled resolution was adopted in an attempt to reconstruct short-term climatic changes during the growing season. The results display a surprising clarity of signal and suggest a significant relationship between δ 13C and relative humidity and, to a lesser extent, temperature. This preliminary study proposes possible reasons for the isotopic profile observed and highlights the perceived future value of intra-ring isotope studies ('microdendroclimatology').

An alternative astronomical calibration of the lower Pleistocene timescale based on ODP Site 677

ABSTRACTOcean Drilling Program (ODP) Site 677 provided excellent material for high resolution stable isotope analysis of both benthonic and planktonic foraminifera through the entire Pleistocene and upper Pliocene. The oxygen isotope record is readily correlated with the SPECMAP stack (Imbrie et al. 1984) and with the record from DSDP 607 (Ruddiman et al. 1986) but a significantly better match with orbital models is obtained by departing from the timescale proposed by these authors below Stage 16 (620 000 years). It is the stronger contribution from the precession signal in the record from ODP Site 677 that provides the basis for the revised timescale. Our proposed modification to the timescale would imply that the currently adopted radiometric dates for the Matuyama–Brunhes boundary, the Jaramillo and Olduvai Subchrons and the Gauss–Matuyama boundary underestimate their true astronomical ages by between 5 and 7%.