• Anti-predation strategy, growth rate and extinction amongst Pliocene scallops of the US eastern seaboard

      Johnson, Andrew L. A.; Valentine, Annemarie; Leng, Melanie J.; Sloane, Hilary J.; Schoene, Bernd; Surge, Donna; University of Derby; University of Loughborough; British Geological Survey; University of Mainz; et al. (2017-06-29)
      Placopecten, Chesapecten and Carolinapecten are scallop genera occurring in the Pliocene of the US eastern seaboard. The first (extant) is a smooth, streamlined form, adept at escaping predators by swimming (‘flight’ strategy). The other two (extinct) are plicate forms. Plication facilitates a ‘resistance’ strategy towards predators which is benefited by large size and high shell thickness - maximally so if these states are achieved early in life. Oxygen isotope profiles show that in early ontogeny, Pliocene Placopecten grew at the same moderate rate as modern Placopecten. By contrast, Chesapecten grew as fast as the fastest-growing modern scallop and developed an unusually thick shell, while Carolinapecten grew substantially faster still, this probably enabled by high primary productivity. Extinction of these genera, and survival of Placopecten, can be attributed to a decline in productivity which prevented a maximally effective ‘resistance’ strategy towards predators but had no deleterious impact on a ‘flight’ strategy.
    • Anti-predation strategy, growth rate and extinction amongst Pliocene scallops of the US eastern seaboard

      Johnson, Andrew L. A.; Valentine, Annemarie; Leng, Melanie J.; Sloane, Hilary J.; Schoene, Bernd; Surge, Donna; University of Derby; University of Loughborough; British Geological Survey; University of Mainz; et al. (2017-07-07)
      Placopecten, Chesapecten and Carolinapecten are scallop (pectinid bivalve) genera occurring in the Pliocene of the US eastern seaboard. The first, present in the area today, is a smooth, streamlined form, adept at escaping predators by swimming (‘flight’ strategy). The other two, which are extinct, are plicate (‘ribbed’) forms. Plication facilitates a ‘resistance’ strategy towards predators which is benefited by large size and high shell thickness - maximally so if these states are achieved early in life. Oxygen isotope (δ18O) profiles show that early ontogenetic extensional growth in Pliocene Placopecten was at the same moderate rate as in modern Placopecten. By contrast, in Chesapecten it was as fast as in the fastest-growing modern scallop (c. 80 mm/annum), and accompanied by development of an unusually thick shell, while in Carolinapecten it was substantially faster still (<140 mm/annum). Rapid growth in Chesapecten and Carolinapecten may have been enabled by high primary productivity, which is indicated by the abundance, diversity and large size of co-occurring vertebrates. The extinction of Chesapecten and Carolinapecten, and the survival of Placopecten, can be attributed to a decline in primary productivity which prevented a maximally effective ‘resistance’ strategy towards predators but had no deleterious impact on a ‘flight’ strategy.
    • Anti-predation strategy, growth rate and extinction amongst Pliocene scallops of the US eastern seaboard

      Johnson, Andrew L. A.; Valentine, Annemarie; Leng, Melanie J.; Sloane, Hilary J.; Schöne, Bernd R.; Surge, Donna; University of Derby; University of Loughborough; British Geological Survey; University of Mainz; et al. (European Geosciences Union, 2017-04-28)
      Placopecten, Chesapecten and Carolinapecten are scallop (pectinid bivalve) genera occurring in the Pliocene of the US eastern seaboard. The first, present in the area today, is a smooth, streamlined form, adept at escaping predators by swimming (‘flight’ strategy). The other two, which are extinct, are plicate (‘ribbed’) forms. Plication facilitates a ‘resistance’ strategy towards predators which is benefited by large size and high shell thickness - maximally so if these states are achieved early in life. Oxygen isotope profiles show that early ontogenetic extensional growth in Pliocene Placopecten was at the same moderate rate as in modern Placopecten. By contrast, in Chesapecten it was as fast as in the fastest-growing modern scallop (c. 80 mm/annum), and accompanied by development of an unusually thick shell, while in Carolinapecten it was substantially faster still (<150 mm/annum). Rapid growth in Chesapecten and Carolinapecten was probably enabled by high primary productivity, for which there is evidence from sediment composition and the associated biota. The extinction of Chesapecten and Carolinapecten, and the survival of Placopecten, can be attributed to a decline in primary productivity which prevented a maximally effective ‘resistance’ strategy towards predators but had no deleterious impact on a ‘flight’ strategy.
    • The cause of late Cenozoic mass extinction in the western Atlantic: insights from sclerochronology

      Johnson, Andrew L. A.; Valentine, Annemarie; Leng, Melanie J.; Surge, Donna; Williams, Mark; University of Derby (The Palaeontological Association, 2014-12)
      Heavy late Cenozoic extinction amongst marine molluscs in the western Atlantic has traditionally been interpreted as a consequence of climatic deterioration. However, the pattern of extinction was not the same in the eastern Atlantic, where conditions also became colder. A fall in primary productivity, suggested by a decline in phosphate deposition, may be the real explanation for western Atlantic extinctions. Evidence in support comes from isotopic- and increment-based (sclerochronological) indications of growth rate in Pliocene scallops. A western Atlantic genus that has survived to the present (Placopecten) had the same moderate growth rate in the Pliocene as now, while two genera that became extinct (Carolinapecten and Chesapecten) had growth rates as fast as any known amongst living scallops. Such rapid growth implies abundant food. Selective extinction of a fast-growing species has also been documented amongst Pliocene oysters in the Caribbean region and attributed to a decline in primary productivity. The likely cause of this is the development of the Central American Isthmus and the consequent reorganization of oceanic circulation in the Gulf of Mexico and wider North Atlantic.
    • Evidence, cause and consequence of exceptionally rapid growth in Pliocene scallops of the US eastern seaboard

      Johnson, Andrew L. A.; Valentine, Annemarie; Leng, Melanie J.; Sloane, Hilary J.; Schoene, Bernd; Surge, Donna; University of Derby (4th International Sclerochronology Conference, 2016-06)
      Scallops are amongst the fastest growing of bivalves, with many species growing in the order of 40 mm per annum in early ontogeny, and reliable evidence of early ontogenetic growth-rates up to 70 mm per annum in wild populations of certain species. From the evidence of oxygen isotope (δ18O) sclerochronology, modern examples of the western Atlantic genus Placopecten grow about 40 mm per annum in early ontogeny. The same approach reveals similar growth rates in Pliocene examples from Virginia and North Carolina. By contrast Pliocene examples of the extinct genera Chesapecten and Carolinapecten from Virginia grew at least 75 mm per annum, faster than has been recorded in any wild modern scallop, and examples of Carolinapecten from Florida grew up to 140 mm per annum, twice the maximum rate in wild modern scallops. The rapid overall growth of Carolinapecten is matched by exceptionally large microgrowth increments. In specimens with the fastest overall growth the number of increments approximately equals the number of days indicated by the oxygen isotopic data (e.g. c. 180 over half an oxygen isotope cycle), implying that deposition was daily. Specimens with slower overall growth do not have smaller increments but have substantially fewer than the number of days indicated by δ18O evidence, showing that reduced overall growth was a consequence of periodic interruptions rather than permanently less favourable conditions. Since few individuals lived more than a year, rapid somatic growth must have been accompanied by gamete production, implying abundant food resources. Intervals of particularly rapid growth (largest microgrowth increments) are fairly closely correlated with increases in δ13C, as might have been caused by phytoplankton blooms. However, there is little evidence that these were stimulated by upwelling since there are few indications of a matching increase in δ18O (i.e. colder water). Instead, primary productivity may have been enhanced by nutrient supply from the land. Whatever the cause of high primary productivity in the Pliocene of the US eastern seaboard, the subsequent demise of two scallop genera with exceptionally rapid growth seems as likely to relate to a decline in productivity as to a fall in temperature.
    • Growth-increment characteristics and isotopic (δ18O) temperature record of sub-thermocline Aequipecten opercularis (Mollusca:Bivalvia): evidence from modern Adriatic forms and an application to early Pliocene examples from eastern England.

      Johnson, Andrew; Valentine, Annemarie; Schöne, Bernd; Leng, Melanie; Sloane, Hilary; Janekovic, Ivica; University of Derby; Nottingham Trent University; University of Mainz, 55128 Mainz, Germany; National Environmental Isotope Facility, British Geological Survey, Keyworth; et al. (Elsevier, 2020-09-02)
      The shell δ18O of young modern Aequipecten opercularis from the southern North Sea provides an essentially faithful record of seasonal variation in seafloor temperature. In this well-mixed setting, A. opercularis shell δ18O also serves as a proxy for seasonal variation in surface temperature. Individuals from less agitated (e.g. deeper) settings in a warm climate would not be expected to record the full seasonal range in surface temperature because of thermal stratification in summer. Such circumstances have been invoked to explain cool isotopic summer temperatures from early Pliocene A. opercularis of eastern England. Support for a sub-thermocline setting derives from high-amplitude variation in microgrowth-increment size, which resembles the pattern in sub-thermocline A. opercularis from the southern Mediterranean Sea. Here, we present isotope and increment profiles from further sub-thermocline individuals, live-collected from a location in the Adriatic Sea for which we provide modelled values of expected shell δ18O. We also present data from supra-thermocline shells from the English Channel and French Mediterranean coast. The great majority of sub-thermocline A. opercularis show high-amplitude variation in increment size, and winter and summer δ18O values are generally quite close to expectation. However, the relatively warm summer conditions of 2015 are not recorded, in most cases due to a break in growth, perhaps caused by hypoxia. The supra-thermocline shells show subdued increment variation and yield isotopic winter and summer temperatures quite close to the local directly measured values. A. opercularis shells therefore provide a fairly good isotopic record of ambient temperature (if not always of relatively warm summer conditions below the thermocline) and their hydrographic setting can be determined from increment data. Early Pliocene examples from eastern England can be interpreted as having lived in a setting below the thermocline, with a higher seasonal range in surface temperature than now in the adjacent southern North Sea.
    • Isotopic temperatures from the early and mid-pliocene of the US Middle Atlantic coastal plain, and their implications for the cause of regional marine climate change

      Johnson, Andrew L. A.; Valentine, Annemarie; Leng, Melanie J.; Sloane, Hilary J.; Schöne, Bernd R.; Balson, Peter S.; University of Derby; University of Loughborough; British Geological Survey; University of Mainz (Society for Sedimentary Geology (SEPM), 2017-04-18)
      Mean seasonal extreme temperatures on the seafloor calculated from the shell δ18O of the scallop Placopecten clintonius from the basal part of the early Pliocene Sunken Meadow Member (Yorktown Formation) in Virginia are very similar to those from the same horizon at the latitude of Cape Hatteras in North Carolina (~210 km to the south). The lowest and highest temperatures calculated from each shell (using δ18Oseawater = +0.7‰) give mean values for winter and summer of 8.4 ± 1.1 °C (± 1σ) and 18.2 ± 0.6 °C in Virginia, and 8.6 ± 0.4 °C and 16.5 ± 1.1 °C in North Carolina (respective median temperatures: 13.3 °C and 12.6 °C). Patterns of ontogenetic variation in δ18O, δ13C and microgrowth increment size indicate summer water-column stratification in both areas, with summer surface temperatures perhaps 6 °C higher than on the seafloor. The low winter paleotemperatures in both areas are most simply explained by the greater southward penetration of cool northern waters in the absence of a feature equivalent to Cape Hatteras. The same current configuration but a warmer general climate can account for the high benthic seasonal range (over 15.0 °C in some cases) but warmer median temperatures (15.7-21.3 °C) derived from existing δ18O data from scallops of the higher Yorktown Formation (using δ18Oseawater = +0.7‰ for the upper Sunken Meadow Member and δ18Oseawater = +1.1‰ for the mid-Pliocene Rushmere, Morgarts Beach and Moore House members). Existing δ18O data from the infaunal bivalve Mercenaria of the Rushmere Member yields a similarly high median temperature (21.6 °C) but a low seasonal range (9.2 °C), pointing to the periodic influence of warm currents, possibly at times when the Gulf Stream was exceptionally vigorous.
    • Seasonally resolved isotopic temperature data as a tool for identifying the cause of marine climate change in the Pliocene

      Johnson, Andrew L. A.; Valentine, Annemarie; Leng, Melanie J.; Sloane, Hilary J.; Schoene, Bernd; Surge, Donna; University of Derby; University of Loughborough; British Geological Survey; University of Mainz; et al. (2017-07-07)
      Alteration in the pattern and vigour of ocean currents has often been invoked as the principal driver of changes in regional climate, including cases in the recent past (Pliocene, Pleistocene and Holocene) and instances predicted in the near future. The theory behind such interpretations is, however, suspect (e.g. Crowley, 1996; Seager et al., 2002), and it may be that other regional or global drivers are more important. The present cool temperate marine climate on the US eastern seaboard north of Cape Hatteras (northernmost North Carolina and Virginia) reflects the influence of cool southward-flowing currents, and a similar influence can be inferred in the Early Pliocene (Johnson et al., 2017). Change to a warm temperate (or marginally subtropical) marine climate in the Late Pliocene has been ascribed to the impingement on the area of warm, northward-flowing currents, assisted by the absence of a barrier equivalent to Cape Hatteras (e.g. Williams et al., 2009). Seasonally resolved oxygen isotope (δ18O) data from bivalve shells reveals, however, that seasonal temperature range was often in excess of that characteristic of the area south of Cape Hatteras (influenced by warm currents), and indicates the continuing influence of cold currents from the north (Johnson et al., 2017). Some isotopic evidence of seasonal temperature range from bivalves is consistent with warm-current influence (Winkelstern et al., 2013), but otherwise the evidence points to a different control (probably global climatic change) on the Late Pliocene warming of marine climate on the US eastern seaboard that is shown by isotopic data for annual average temperature. References: Crowley, T.J. (1996) Pliocene climates: The nature of the problem. Marine Micropaleontology, 27, 3-12. Johnson, A.L.A., Valentine, A., Leng, M.J., Sloane, H.J., Schöne, B.R., Balson, P.S. (2017) Isotopic temperatures from the Early and Mid-Pliocene of the US Middle Atlantic Coastal Plain, and their implications for the cause of regional marine climate change. PALAIOS, 32, 250-269. Seager, R., Battisti, D.S., Yin, J., Gordon, N., Naik, N.H., Clement, A.C., Cane, M.A. (2002) Is the Gulf Stream responsible for Europe's mild winters? Quarterly Journal of the Royal Meteorological Society, 128, 2563-2586. Williams, M., Haywood, A.M., Harper, E.M., Johnson, A.L.A., Knowles, T., Leng, M.J., Lunt, D.J., Okamura, B., Taylor, P.D., Zalaziewicz, J. (2009) Pliocene climate and seasonality in North Atlantic shelf seas. Philosophical Transactions of the Royal Society of London, Series A, 367, 85–108. Winkelstern, I., Surge, D., Hudley, J.W. (2013) Multiproxy sclerochronological evidence for Plio-Pleistocene regional warmth: United States Mid-Atlantic Coastal Plain. PALAIOS, 28, 649-660.
    • The use of seasonally resolved temperature data to identify the cause of marine climate change

      Johnson, Andrew L. A.; Valentine, Annemarie; Leng, Melanie J.; Sloane, Hilary J.; Schöne, Bernd R.; Surge, Donna; University of Derby; University of Loughborough; British Geological Survey; University of Mainz; et al. (European Geosciences Union, 2017-04)
      On the continental shelf of the eastern USA, seasonal variation in water temperature is much lower south of Cape Hatteras than it is to the north as a result of the influence of warm currents, which raise winter temperature. High temperatures north of Cape Hatteras during the Pliocene have been attributed to greater northward penetration of warm currents in the absence of a feature analogous to Cape Hatteras. However, oxygen isotope thermometry using serial ontogenetic samples from scallops reveals a high seasonal temperature range at some horizons, suggesting that overall warming was the consequence of general climate change, with the absence of a ‘Cape Hatteras’ feature allowing greater southward penetration of cold currents, resulting in low winter temperatures at a southerly latitude. Evidence from other taxa indicates that at times seasonal variation in water temperature was quite low and that there was greater northward penetration of warm currents. This may relate to increases in vigour of the Gulf Stream. The study shows how seasonally resolved temperature data can assist identification of the driving forces of marine climate change.