Paleoclimates and Paleoenvironments - a Summary of Workshop Discussions

The ostracode record is a valuable source of information about past climates and paleoenvironments.  A long publication history of excellent studies has shown how valuable these records are in regional studies of the Quaternary.  Here, the workshop discussions focused on future research initiatives that could best make use of the existing foundation of regional studies, and thus move forward in understanding continental and hemispheric scale processes.  Also, underdeveloped research areas critical to our understanding of hemisphere scale processes were discussed.

A.  Future Research Initiatives

1.  Northern Hemisphere Mapping of Ostracode Species-this biogeographic initiative will be the basis for numerous subsequent investigations into paleoclimatic significance, genetic and phylogenetic patterns, biodiversity, and anthropogenically driven environmental impacts.  To date, studies of nonmarine Quaternary ostracodes have tended to be regional in scope.  The community is ready to move forward to the trans-regional, hemispheric scale of biogeographic analysis.    Just as other proxies for past climates and environments have been mapped across regions (such as pollen, diatoms, and vertebrates), so too must ostracode data be examined in a similar way.  The hemispheric view will allow us to see large scale climatic processes reflected in ostracode distributions that are simply not visible in any other way.  Specifically, begin with a focus on a few key taxa with potential trans-regional or hemispheric distribution, such as Limnocythere inopinata, Cytherissa lacustris, or Candona candida.  Expanding available datasets to include estuarine and coastal species is important in this mapping initiative, as is working in tandem with the development of quantitative methods for assessing climatic and environmental significance.  New quantitative methods (e.g., MOTR method, Horne, 2007) as well as existing methods involving transfer functions and modern analog techniques (see Smith, 2012 for a summary) should be applied to ostracode datasets as part of multi-proxy analyses.

2.  Ground water - Surface Water Interactions - this initiative will involve hydrologic and geochemical investigations in tandem with ostracode ecology in a variety of settings.  Ostracodologists have noted in numerous publications (for a review and summary, see Smith & Palmer, 2012)  that local to regional groundwater discharge patterns have a profound influence on surface water bodies and their ostracode assemblages, such that considerable variation can exist on the local scale when all other factors of climate and landscape are the same.  These processes influence the paleoclimate record as tracked by ostracodes and their geochemical and isotopic signatures.  Thus ostracodes can track subtle variations in hydrology that are the result of process dynamics of regional hydrologic and climatic interactions.

3.  Past Interglacials and Non-Analog Assemblages - Published ostracode records of numerous interglacial stages exist, yet little has been done to synthesize these data with other proxies. Ostracodologists can provide important environmental and climate data about previous interglacials in ways that other biological proxies cannot do, and offer valuable calibration data for climate models.   Recently, PAGES presented a report "Investigating Past Interglacials: An Integrative Approach" (learn more here)  and we should consider how the ostracode record fits into projects of this kind and what new information we can bring forward (quite a lot, particularly about older interglacials!).  In particular, we need to address the problem of non-analog assemblages, which are a feature identified in all of the biological climate proxies (pollen, diatoms, vertebrates, etc.) Non-analog assemblages are important indicators of unusual climate states or abrupt climate change.  More collaborative multi-proxy work should be pursued to gain the most information about unfamiliar climate states from past interglacials, as identified from these assemblages.  

B.  Underdeveloped research areas with high potential for breakthroughs in paleoclimatic and paleoenvironmental processes

1.  Groundwater Ecology and Ostracodes-Well developed studies exist in western Europe, where regulated rivers along international boundaries have led to considerable investment in groundwater monitoring.  Outside of western Europe, little has been done to explore the ostracode fauna of oxygenated aquifer systems (recent studies in Australia point towards considerable hypogean species diversity - see Reeves et al., 2007) .  Shell geochemistry (isotopes, trace elements), along with ecological and genetic studies, should be undertaken to better understand the significance of hypogean fauna such as aquifer taxa.  Development of baseline data on ostracodes in modern aquifers might show otherwise hidden biodiversity, as well as provide new biomonitors of water quality.  Genetic analysis could provide estimates of when these fauna invaded aquifer systems (multiple invasions?), and whether endemic or cosmopolitan fauna are typical. 

2.  Biogeographic Parthenogenesis-The ostracode record provides numerous examples of biogeographic parthenogenesis that may be linked to evolutionary ecological processes, including climate forcing.  Considerable research has been conducted in Europe on this topic, but few studies have been done on the North American fauna, which shows many examples of this phenomenon.  The North American fauna, when considered in the light of hemispheric and/or global distributions, may provide important keys to the question of reproductive strategies as influenced by climatic and environmental change.  Collaborative research  involving genetics, paleontology, and climate modeling could provide breakthroughs in our understanding of this reproductive pattern.  Related to this topic is that of the role of refugia in ostracode diversity.  Again, more studies have been published on European taxa (see, for example, Schön, 2007) than in North America.

C.  Recommendations - Collaboration with the Wider Scientific Community is Needed.

1.  Extend the Quaternary ostracode community by seeking out Russian and Chinese scholars-we need their expertise to explore hemispheric and global climate signals and to develop trans-regional paleoecological interpretations.

2.  Expand existing non-marine datasets to include coastal and estuarine species.

3.  Include existing isotopic and trace element data associated with species data in contributions to larger databases.

4.  Establish data collection and recording standards to minimize difficulties in migrating data to large databases (see Taxonomic Harmonization page).

5.  Get started by pursuing taxonomic harmonization of key taxa with significant value in paleoclimatic and paleoenvironmental interpretations, such as Limnocythere inopinata, Cytherissa lacustris, and Candona candida, among others (see Taxonomic Harmonization page)

6.  Collaborate more widely in multi-proxy (biological and geochemical) studies and climate model calibration studies.

D.  References

Horne, D., 2007.  A mutual temperature range method for Quaternary paleoclimatic analysis using European nonmarine Ostracoda, Quaternary Science Reviews, 26, 1398-1415.

Reeves, J.A., De Deckker, P. and Halse, S.A., 2007.  Groundwater ostracods from the arid Pilbara region of northwestern Australia: distribution and water chemistry, Hydrobiologia, 585, 99-118.

Schön, I., 2007.  Did Pleistocene glaciations shape genetic patterns of European ostracods?  A phylogeographic analysis of two species with asexual reproduction, Hydrobiologia, 575, 33-50.

Smith, Alison J., 2012. Evidence of environmental change from terrestrial and freshwater palaeoecology, Chapter 12 IN (Matthews, J., Bartlein, P., Briffa, K., Dawson, A., de Vernal, A., Denham, T., Fritz, S. and Oldfield, F.,  Eds.) , Handbook of Environmental Change, Sage Publishing, pp. 254-283.

Smith, A.J. and Palmer, D.F. 2012. The versatility of Quaternary ostracods as palaeoclimate proxies: comparative testing of geochemical and ecological/biogeographical approaches,  IN (Horne, D., Holmes, J., Rodrigez-Lasaro, J., and Viehberg, F., Eds.) Ostracoda as Proxies for Quaternary Climate Change, vol. 17 in Developments in Quaternary Science series, Elsevier Science Publishing, pp. 183-203.

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