Editorial: North Pacific Environment and Paleoclimate from the Late Pleistocene to Present
- 1Florence Bascom Geoscience Center, United States Geological Survey (USGS), United States
- 2Geosciences and Environmental Change Science Center, United States Geological Survey, United States
- 3Goddard Institute for Space Studies (NASA), United States
The vast area of the North Pacific, spanning ~55˚ longitude, represents a challenge for documenting and understanding the geologic history of ocean, atmosphere, and terrestrial environmental change. This special issue highlights site-specific analyses to address these questions and provides clues that arise in response from continued North Pacific warming today in a rapidly changing climate (Fig. 1). The emergence of new methods and novel application of existing methods serve to enhance our fundamental understanding of natural modes of climate variability driven by ocean and atmospheric circulation patterns, including the role of external (e.g., insolation) versus internal forcing (e.g., El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO)). Included in this volume are geographically diverse studies that present new and traditional methods for the interpretation of climate records drawn from pollen, macrofossils, tree rings, diatoms, grain size, and glacial studies. Many provide new geographic comparisons, such as Kamchatka and Hawaii, or emerge from novel geologic archives and environments, such as the marine shelf, a thermokarst lake and a fossil forest.Questions of natural variability targeted in the compendium include:• What are geographic patterns of temperature and moisture variability since deglaciation?• How does carbon accumulation compare among wetlands throughout the North Pacific, and how does moisture affect the differences in accumulation rates?• What role does seasonality play in the temperature and moisture balance of a region?• What are the primary controls on glacial advance in non-tidal glaciers of the North Pacific coast?• Do productivity patterns in the ocean and land show synchronous response to climate variability?• What are the relationships between patterns of thermokarst modification and changes in climate, forest growth, and fire regimes?• How can lake basin morphology affect shifts in mixing depths, which impact diatom paleorecords?We solicited studies from across the entire North Pacific. The studies range from the Hawaiian Islands in sub-tropical North Pacific (Beilman et al., 2019), California and Montana in midlatitude eastern Pacific (Carlin et al., 2019: Kirby et al., 2019Stone et al., 2019) A brief summary of each submission to this volume is provided below. • Carlin et al examine grain size and chronology ( 210 Pb, 137 Cs, 14 C) in four cores from Monterey Bay, California, in order to investigate shelf sedimentation and ways in which it is affected by climate and humans. They conclude that during dry climatic intervals, sedimentation is dominated by coastal erosion rather than by riverine inputs. In contrast, during wet years more sand was transported from rivers than from coastal erosion to the shelf. They also conclude that dams created by humans contribute to more coastal erosion, and to transport of more littoral sediment offshore.• Kirby et al. explore Holocene lake level variations in drought sensitive southern California using paleo lake water isotope ratios captured by sedimentary carbonate. In tandem with sediment grain size variations, a proxy for winter precipitation amounts, the extent of water isotope evaporative enrichment indicated by calcite oxygen isotopes is used to provide companion proxies for summer effective moisture. The combined data provide an enhanced record of drought that illustrates the relative effects of changes in seasonal moisture availability.• Stone et al. utilize diatom-inferred lake mixing depth reconstructions in mountain regions of Montana to explore the extent of regional hydroclimatic variability during the Holocene by examining the influence of individual lake bathymetry. They show that the effects of complex basin morphometry on mixing depth varies with lake levels, thereby complicating interpretation of lake level trends from diatom data. Recognition of unique morphometric effects are found to resolve apparently contradictory late Holocene hydroclimatic trends and provide a new methodological approach that will benefit future work.• Berkelhammer uses satellite-derived Solar-Induced Florescence and chlorophyll-alpha as proxies for land and sea productivity to determine whether marine-terrestrial synchrony is a widespread phenomenon during modes of climate variability, such as El Nino Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). He finds that marine and terrestrial ecosystems are synchronous across thousands of miles of the North Pacific coastline and that the strength of the synchrony depends on the relative states of the PDO and ENSO. He proposes reasons and implications for the observed pattern.• Peteet et al. focus on western Kodiak Island peatlands, where a 16,000 -year carbon sequestration record is coupled to the vegetational and isotopic history. During cooler, drier climate such as the Younger Dryas, the records show a decline in carbon stored, while the wet and warm early Holocene produces maximum values. A very large deuterium/hydrogen isotopic shift in the mid-Holocene (6, 500 yr BP) suggests that moisture arrived from cooler waters or a more distal source. Neoglaciation about 3700 years ago brings cooler conditions as Artemisia, Betula, and Sphagnum increase, and carbon sequestration increases, all linked to the intensification of the Aleutian Low.• Jones et al. conduct an oxygen isotope analysis of modern peatland water-plant relationships to better understand the relationship of peatland water to precipitation, and how plant cellulose oxygen isotope differences differ in their offset to peatland water depending on species and location within a peatland. They determined that bryophytes (non-vascular) were not statistically different from one another, but that sedges (vascular) were offset from bryophytes. They use this information to re-evaluate results of a previously published peat oxygen isotope record, which has implications for the deglacial and Holocene evolution of the Aleutian Low in southcentral Alaska. This study also proves the utility of this novel proxy for paleo-hydroclimatic studies in the North Pacific.• Ager provides a comprehensive overview of the southeastern Alaskan paleoecological history, including three new palynological records from the region. Hummingbird Lake, southwestern Baronov Island, begins about 15,000 years ago and mirrors the sequence of vegetational change found in previous regional cores. Two nearby marine records, though younger, provide similar complementary pollen sequences. His paper elucidates regional links between these records and possible tree refugia, the Queen Charlotte Islands to the south, and early human colonization.• Gaglioti et al. approach questions about late Holocene glacier activity in the St. EliasMountains from a recently exposed "ghost", or fossil, forest located on the south-central coast. Utilizing dendrochronological cross-dating methods, comparisons with Little Ice Age chronologies from nearby glaciers, and paleoclimatic data, they explore the climate variables that may have controlled glacier fluctuations in the region. These comparisons are used to examine the prominent differences between the timing of Little Ice Age advances in Alaska and North Atlantic regions to propose the importance of winter precipitation for Gulf of Alaska glaciers during the 19 th century.• Bigelow et al. relate the vegetational and climate history from four lakes in the middle Susitna Valley, Alaska, to human occupancy in the region. Their multidisciplinary research includes pollen, diatoms, and geochemistry. Shrub tundra characterized the earliest vegetation about 12,000 years ago, followed by a possible Younger Dryas cooling and aridity, then subsequent warming in the early Holocene as forest advanced beyond present limits. Retreat of spruce after 4500 years ago indicates late Holocene cooling.• Anderson et al. explore Holocene thermokarst lake development and evolution in discontinuous permafrost landscape of northern Interior Alaska. The study highlights thermokarst evolution that is characteristic of loess uplands -a landscape that is widespread and yet frequently overlooked for paleoclimatic studies. The authors propose that initial thermokarst lake formation and expansion occurred during early Holocene warmth, corresponding with boreal forest and fire development. Following a period of stabilization, subsequent lake-level rise and fall were influenced by climate via groundwater-surface water dynamics and North Pacific atmospheric circulation variability.• Nichols et al. use stable isotope geochemical and plant microfossil record from a peatland in Kamchatka, Russia to examine hydroclimate variability and the controls on that variability in the northwestern Pacific. They find a generally wetter early and late Holocene with a drier, more episodic precipitation regime during the mid-Holocene. These patterns are similar to patterns recorded in the eastern North Pacific, as well as northern Japan. They conclude that the observed patterns can in part be explained by changes in tropical Pacific sea surface temperatures, highlighting the potential influence of the tropics across the broader North Pacific region.
Keywords: paleoclimate, North Pacific, Proxy, Hydroclimate, Holocene
Received: 23 Oct 2019;
Accepted: 28 Oct 2019.
Copyright: © 2019 Jones, Anderson and Peteet. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Dr. Miriam C. Jones, Florence Bascom Geoscience Center, United States Geological Survey (USGS), Reston, United States, firstname.lastname@example.org