Identifying New Community-Driven Science Themes for NSF's Support of Paleoclimate Research Proceedings of a Workshop (2021) / Chapter Skim
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Glacial, Ocean, and Land Processes and Feedbacks
Glacial, Ocean, and Land Processes and Feedbacks
Pages 25-46
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From page 25... ...
They also considered the types of feedbacks that are operating in different components and the proxies that researchers can use to reconstruct those changes. Specifically, workshop participants discussed ice-sheet and high-latitude proxies and feedbacks, including sea level; ocean proxies and feedbacks, including ocean circulation and changes to biochemistry and productivity; and terrestrial proxies and feedbacks, including fire and vegetation dynamics and the terrestrial carbon cycle.
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From page 26... ...
While polar ice sheets are expected to become the dominant contributor to global mean sea-level rise in the 21st century, projections of the magnitude and rate of sea-level rise include assumptions about the link between sea level and global temperatures in the past and an incomplete understanding of the complex processes involved in rapid ice-sheet retreat (Rignot et al., 2014)
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From page 27... ...
In order to get to the precision and level of detail in paleo reconstructions needed to inform future climate projections, revisiting and remapping sites with better chronological technologies to get higher quality data could be useful. In the breakout session on sea level, ice sheets, and GIA, moderated by Paul Bierman, University of Vermont, and Andrea Hawkes, University of North Carolina Wilmington, participants also discussed the need to do sea-level benchmarking in projection models to better articulate sea-level changes to policy and decision makers (Figure 9)
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From page 28... ...
Similar to glacial isostatic adjustment, dynamic topography is a process resulting in long-term deformation of the Earth's surface, which influences sealevel reconstructions in the past, typically > 100,000 years and earlier. Using a combination of modeling and data comparison to understand longer term deformation, as driven by mantle convection, tectonics, sediment loading, and other factors, is needed to reconstruct sea level in the past, as deformation associated with these processes can be at the multi-meter level.
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From page 29... ...
More direct observations of ice-sheet history, particularly during interglacial periods, could help answer these questions, including rock samples from beneath today's ice sheets, drills that can access the ice-sheet bed, and offshore records adjacent to Greenland and Antarctica. Participants in the breakout session echoed the need for new, fast coring systems and offshore marine records, paired with sediment provenance data to help determine paleo ice-sheet extent and ice-sheet source and flow dynamics.
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From page 30... ...
, and Joseph Ortiz, Kent State University, participants also discussed the need to focus on pre-LGM warm periods and, specifically, to explore how the Arctic and sub-Arctic outside of the North Atlantic, and their teleconnections with low latitudes, change during periods of rapid change and previous warm periods. Amelia Shevenell, University of South Florida, added that, for the Antarctic Ice Sheet, ice-sheet evolution at catchment scale during warm climate intervals remains a knowledge gap, but records of these warm periods are more likely to be preserved on the continental shelf.
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From page 31... ...
In the Antarctica and Southern Ocean processes breakout session, moderated by Julia Wellner, University of Houston, and Liz Sikes, Rutgers University, participants also discussed the need to understand past glacial ice extent from the terrestrial perspective, and sea-ice extent from the marine perspective. For both terrestrial and marine records, more temporal and spatial data may be essential, beyond the wellstudied regions of the Atlantic and West Antarctic Ice Sheet and multiple catchment and basin studies.
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From page 32... ...
Many workshop participants discussed the importance of community engagement before having funding or a proposal in mind, but acknowledged that visits to regions like the Arctic can be cost prohibitive, especially for early career researchers: dedicated funding mechanisms for these activities could be helpful. OCEAN PROXIES AND FEEDBACKS Sediments preserved in ocean basins have accumulated over time and have recorded detailed information about the role of the ocean in the Earth system, the response of the ocean to forcings, and the complexity of internal system feedbacks of ice-ocean-carbon cycle interactions.
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From page 33... ...
The ratios of oxygen isotopes present in these shells vary in response to changes in global ice volume and ocean temperature, and isotopes of carbon indicate the transfer of organic material among reservoirs on land, in the ocean, and in the atmosphere. Similar to pollen found in terrestrial sediments, these shell-forming phytoplankton and zooplankton are abundant and widely distributed, and their modern climate preferences are often well known; therefore, the assemblages of plankton populations identified in marine sediment records can also be used to reconstruct past climates in archives millions of years old.
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From page 34... ...
The internal system feedbacks of iceocean-carbon cycle interactions, which are crucial, are not currently captured by models. Schmittner suggested that low-resolution Earth system models could be used to fully couple components of the system to interactive ice sheets and oxygen isotopes in those ice sheets.
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From page 35... ...
Glacial, Ocean, and Land Processes and Feedbacks 35 BOX 8 Sharing Knowledge with Community Databases Lawrence pointed out the importance of developing tools to collate and access published data in order to identify data gaps and serve as a launchpad for synthesis work that can facilitate understanding of mechanisms and interface with models. Examples include paleo-co2.org (Figure 4, p.
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From page 36... ...
, for which there was more interest compared to the common era or past cold periods. Responses indicated the large number of unanswered questions about warm periods that may be useful for anticipating future climate.
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From page 37... ...
Walczak pointed to evidence that challenges the AMOC-centric view of the previous decade, in which destabilization of Pacific ice sheets and changes in Pacific Ocean circulation reliably precede similar changes in the North Atlantic. With global oceans being most strongly connected in the south, efforts also could be directed towards understanding the role of Antarctic climate in modulating global climate change, considering that surface temperatures in the Southern Ocean may be a major factor in variability of heat content in the whole ocean, though it is still not understood how that transfer of heat happens (Baggenstos et al., 2019; Clark et al., 2018; Shackleton et al., 2020)
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From page 38... ...
Ocean Productivity and Biochemistry The ocean productivity and biochemistry breakout group moderated by Christopher Hayes, University of Southern Mississippi, and Summer Praetorius, USGS, discussed overarching, outstanding questions of ocean productivity: How is primary productivity linked to export productivity, and what are the drivers of abrupt changes in ocean productivity, including shortterm feedbacks and timescales for recovery? Because ecological changes in the ocean will have impacts on the climate system, participants discussed investigating whether abrupt changes in marine ecosystems are integral to abrupt climate changes in the past.
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From page 39... ...
TERRESTRIAL PROXIES AND FEEDBACKS During this session, workshop participants focused on terrestrial proxies and feedbacks related to fire dynamics, vegetation dynamics, and the global carbon cycle. Examples of proxy records that can be used to understand these systems include tree rings, charcoal, peat sediments, speleothems, and biomarkers.
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From page 40... ...
Paleo-fire and paleo-vegetation proxy records -- including fire scars in trees; charcoal, biomarkers, and pollen in lake sediments, peat, and ocean sediments; and gases and aerosol tracers in glacier ice -- are used to quantify past fire emissions and their drivers. Given the importance of emissions, participants in the fire and vegetation breakout discussion, moderated by Cathy Whitlock, Montana State University, and Mary Edwards, University of Southampton, described how linking emissions information with the paleo fire record may be useful -- for example, assessing emissions by comparing marine and terrestrial records to understand the scale of fire feedbacks into the atmosphere.
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From page 41... ...
Specifically, for research questions around fire, participants discussed the importance of learning from indigenous knowledge and co-constructing scientific questions with communities affected by fire. The carbon cycle breakout session discussed opportunities for cross-community interactions to examine questions of seafloor inputs and outputs by working with the oceanographic community and incorporating more complex information into geochemical modeling for carbon cycling on the seafloor.
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From page 42... ...
The rate of carbon release is a major difference between the past and future, but there is limited knowledge about the response of permafrost to past warming, making it difficult to evaluate the permafrost carbon feedback in the future. Walter Anthony highlighted knowledge gaps in the permafrost carbon feedback from the last deglaciation (21,000 years ago)
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From page 43... ...
Participants in the terrestrial and ocean carbon cycle breakout session, moderated by Matthew Winnick, University of Massachusetts Amherst, also discussed the need for better understanding land-atmosphere feedbacks, specifically the coupling of CO2 and water, in order to constrain tropical carbon cycle dynamics, which includes attention to reconstructing past climates in the tropics, and leveraging remote sensing of modern carbon pools.
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From page 44... ...
There also could be opportunities to examine carbon cycle dynamics during transitions from hot to cold states, as well as to focus on transition zones between the terrestrial and oceanic environment. Workshop participants also discussed interest in better characterizing the role of carbon cycle processes traditionally thought of as long-term or geologic on shorter timescales and under evolving climate states, particularly processes thought of as being imbalanced, and how they may have driven climate changes in the past.
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From page 45... ...
BOX 11 Reflections from the Early Career Breakout Discussion Workshop planning committee members Tripti Bhattacharya, Syracuse University, and Kau Thirumalai, University of Arizona, summarized the main takeaways from the early career breakout session, which was geared towards late stage Ph.D. students and postdocs.
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