Reconstructing postglacial hydrologic and environmental change in the eastern Kenai Peninsula lowlands using proxy data and mass balance modeling
Abstract
Despite extensive paleoenvironmental research on the postglacial history of the Kenai Peninsula, Alaska, uncertainties remain regarding the regions deglaciation, vegetation development, and hydroclimatic history. Efforts to identify regional climate patterns are confounded by the challenge of teasing apart the variables that influence these sedimentary proxy records. To disentangle some of these variables at two sites in this region, we present new proxy datasets from Hidden and Kelly Lakes, located in the eastern Kenai lowlands near the Kenai Mountains, including sedimentological properties, pollen and macrofossils, diatom assemblages, and diatom oxygen isotopes. We also use a simple hydrologic and isotope mass balance model to constrain our interpretations of the diatom oxygen isotope data. Using this multi-pronged approach, we identify dominant drivers of postglacial change, and propose the most plausible paleoenvironmental scenarios that gave rise to the observed proxy data. Glacier ice retreated from the catchment of Hidden Lake at ~13.1 ka cal BP. In the early Holocene (~10 9 ka cal BP), groundwater was likely an important component of the hydrologic budget at Kelly Lake, and the lake was likely shallower compared to present day. From 9 7 ka cal BP, the arrival of Alnus (alder) followed by Picea (spruce) was associated with higher productivity in the lakes, as well as better-developed soils and a lower contribution of groundwater. From 7 5 ka cal BP, lake level likely increased at Kelly Lake, and by 5 ka cal BP it had likely reached or exceeded its modern level. In the last ~75 years, modern climate change has caused increased biogenic silica content and decreased diatom oxygen isotope values. These results highlight: 1) the utility of simple mass balance modeling to constrain interpretations of paleo oxygen isotope data; 2) the utility of a multi-site, multi-proxy approach for gaining a holistic understanding of past hydrologic and environmental change; 3) the importance of groundwater as an influence on lake water isotope composition, especially for lakes situated near glaciated mountain fronts; and 4) the potential of site-specific responses to confound interpretations of regional climate phenomena, suggesting that paleo datasets should be interpreted with site-specific factors in mind.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMPP43B..07B