Filling a Geographical Gap: New Paleoecological Reconstructions From the Desert Southwest, USA

Abstract

In 1916 the time stamp for quantitative palynology was set with Lennart von Post's initial paper on pollen analysis and environmental change in the Scandinavian peat bogs. In the 1930s, Von Post provided a map of the known palynological reconstructions. This map showed many conspicuous gaps of geographic coverage that have endured to this day. In particular, environmental reconstruction in arid lands remain much less known, largely due to the paucity of depositional environments in these areas as well as challenges with preservation in regions either uniformly dry or subjected to strong wet/dry phases. Over the last decade we have examined linkages between desert wetland development and episodes of wet and arid conditions. Desert wetland, or ciénegas, are recharged by groundwater and appear to be sensitive to climate-driven groundwater fluctuations. These systems appear to "grow" during wet periods potentially associated with enhanced El Niño activity, suggesting an important linkage with groundwater dynamics and the quantity and frequency of winter precipitation delivery. Hydrologic conditions in ciénegas are also important controls on the preservation of pollen, where episodes of aridity coincide with periods of poor pollen preservation. We assess modern El Niño events, as analogs of past wet conditions, to provide context on the atmospheric controls for delivery of moisture into the desert southwest during winter. Our analysis shows that anomalously high and persistent moisture delivery into the region during El Niño events enables the growth of ciénegas, improves preservation of pollen and promotes the growth of fuels necessary to support wildfire. This paper examines ciénega sites located in the southwestern region of North America at the US/Mexico Border and discusses results that addresses a geographical gap identified by Von Post's original work in paleoenvironmental research.

Effects of Holocene climate change, volcanism and mass migration on the ecosystem of a small, dry island (Brava, Cabo Verde)

“…As a consequence we have limited understanding of long‐term ecological dynamics in these locations. Dry sediment archives such as volcanic calderas are the alternative, yet they are more likely to be affected by interrupted sedimentation and uneven and discontinuous preservation of microfossils (Brunelle et al, 2018; Carrión et al, 2009). However, we demonstrate that sites such as this highland volcanic caldera hold a diversity of forms of palaeoenvironmental information.…”

“…A comparison of disturbance dynamics before and after human arrival can increase our understanding of how human impacts overprint –or interact with– naturally occurring features of the island environment (Dearing et al, 2006; Paine et al, 1998). It is particularly challenging to develop records of long‐term environmental change in dry regions due to poor microfossil preservation and a scarcity of undisturbed sediment archives (Brunelle et al, 2018). Nevertheless, palaeoecological research carried out in dryland soil stratigraphic sequences can provide an essential historical perspective on ecological change in dry islands (e.g.…”

Holocene upland and wetland dynamics in the Chihuahuan Desert, Cuatrociénegas Mexico

“…Long-lived desert wetlands, or ciénegas, are widely distributed in northern Mexico and the southwestern United States (Hendrickson et al, 2021;Middleton et al, 2022). These environments have been a good source of paleoenvironmental data that is stratigraphically constrained (Brunelle et al, 2014(Brunelle et al, , 2018Davis et al, 2002;Minckley and Brunelle, 2007;Minckley et al, 2009Minckley et al, , 2011Minckley et al, , 2013Minckley et al, , 2019. However, as in other arid contexts, these environments are subject to desiccation that can result in pollen samples with poor preservation and high indeterminate counts that make working with ciénega records difficult and require analytical creativity (Florenzano et al, 2019;Horowitz, 1992;Minckley and Brunelle, 2007;Minckley et al, 2011Minckley et al, , 2013.…”

“…nest material, found throughout the North American Deserts and used to characterized major environmental changes over the past 40,000 years (Betancourt et al, 1990). While the development of environmental histories from new pack-rat records has tapered off in the past few decades, refreshed interest in desert sedimentary records has emerged (Brunelle et al, 2018; Metcalfe, 2006; Metcalfe et al, 2000; Minckley et al, 2019).…”

A 1200-year history of environmental changes in Bay Jimmy area, coastal Louisiana, USA

“…The disappearing wetlands, such as those of Bay Jimmy area, Louisiana, are great repositories of proxies for reconstruction of past environments, including storm events. The wetlands offer excellent preservation environment for pollen and other palynomorphs, which are superb for paleoenvironmental reconstruction (Brunelle et al, 2018;Dark, 2017aDark, , 2017b. The loss of wetlands severely threatens the integrity of these archives for paleoenvironmental histories.…”