The results from this study show that analytical size fraction choice is a key determinant of diversity signals in deep-time and furthermore it is small species that maintain ecological function during transient climatic events. I created a diversity record of planktonic foraminifera through the Middle Eocene Climatic Optimum comprising of 22,800 individuals classified to three taxonomic levels and investigated the responses of these assemblages using effective diversity: a novel approach for Palaeogene and deep-time systems (Chapter 2).
The primary objective of this thesis is to measure and understand the relationship between planktonic foraminifera and their environment, to enable a more biologically informative assessment of the fossil record. The high spatial and temporal resolution of the planktonic foraminifera fossil record provides an ideal system to investigate ecosystem responses to climatic fluctuations at multiple scales and levels. How we utilize the fossil record is therefore of critical Importance. The fossil record can provide us with a means of investigating ecosystem responses to long-term climatic fluctuations which can act as baselines for future anthropogenic induced change. What is unknown is how biotic communities and ecosystems will react to this change on both short and long timescales. Overall, high abundances and carbon biomass were derived from the euphotic zone and equatorial region of the Eastern Indian Ocean. The Pearson correlation analysis showed that the temperature and chlorophyll-a were two explanatory environmental variables that were found to be highly significant (p < 0.05) and that triggered the distribution and abundance of dominant foraminifera species in the study region. calida 0.68 µg C m−3, Trilobatus sacculifer 0.38 µg C m–3, Orbulina universa 0.56 µg C m–3, and G. Due to its large size, Globorotalia menardii had total carbon biomass of 3.9 µg C m–3, followed by G. The high carbon biomass was recorded at two stations in the equator zone. The shell size of collected taxa was from 51 to 508 μm and the total carbon biomass was estimated to be between 0.062 µg C m–3 and 26.52 µg C m–3. Dominant species that were characterized by the high dominant index Y > 0.14–0.46 were Globigerina bulloides, Globigerinoides ruber white, Globigerinella siphonifera, Turborotalita quinqueloba, and Globigerinella calida, contributing to the community up to 86%. A total of 20 taxa were identified based on the spherical chamber shell, spines, and a final whorl which were examined under light microscopy and scanning electron microscopy. The temperature (☌) ranged between 12.82 and 31.8 ☌, the salinity ranged between 32.5 and 35.5, and chlorophyll-a concentrations ranged between 0.005 µg/L and 0.89 µg/L. Foraminifera species were collected through plankton net sampling at 44 locations (80.00°–96.10° E, 10.08° N–6.00° S). These results suggest the diversity patterns of planktonic foraminifera cannot be explained by any one environmental variable or proposed mechanism, but instead reflect multiple processes acting in concert.ĭistribution and carbon biomass of planktonic foraminifera were investigated from the euphotic zone of the Eastern Indian Ocean during a two-month cruise, ‘Shiyan I’ (10 April–).
The evolutionary mechanism of deep-time stability finds mixed support whilst there is relatively little evidence for an out-of-the-tropics model. There is evidence for functional redundancy in the low-latitude sites. There is limited evidence that seasonal turnover explains diversity patterns. Vertical structure could be linked to increased diversity through the strength of stratification, but not through the depth of the mixed layer. Sea-surface temperature explains the largest portion of diversity in all four diversity measures, but not in the way predicted by the metabolic theory of ecology. Spatial autoregressive models showed that the same broad suite of environmental variables were important in shaping each of the four largely independent diversity measures (rarefied species richness, Simpson’s evenness, functional richness and mean evolutionary age). Environmental variables chosen to capture ocean temperature, structure, productivity and seasonality were used to model a range of diversity measures across the world’s oceans. Within this group, marine surface sediment assemblages are thought to represent an accurate, although centennial to millennial time-averaged, representation of recent diversity patterns.
This study tests the set of ecological and evolutionary hypotheses proposed to explain the global variation in present-day coretop diversity in the macroperforate planktonic foraminifera, a clade with an exceptional fossil record.
Global diversity patterns are thought to result from a combination of environmental and historical factors.
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