Clim. Past, 13, 1355–1379, 2017 https://doi.org/10.5194/cp-13-1355-2017 © Author(s) 2017. This work is distributed under the Creative Commons Attribution 3.0 License. Climatic history of the northeastern United States during the past 3000 years Jennifer R. Marlon1, Neil Pederson2, Connor Nolan3, Simon Goring4, Bryan Shuman5, Ann Robertson1, Robert Booth6, Patrick J. Bartlein7, Melissa A. Berke8, Michael Clifford9, Edward Cook10, Ann Dieffenbacher-Krall11, Michael C. Dietze12, Amy Hessl13, J. Bradford Hubeny14, Stephen T. Jackson3,15, Jeremiah Marsicek5, Jason McLachlan16, Cary J. Mock17, David J. P. Moore18, Jonathan Nichols19, Dorothy Peteet19, Kevin Schaefer20, Valerie Trouet21, Charles Umbanhowar22, John W. Williams4, and Zicheng Yu6 1Yale School of Forestry and Environmental Studies, New Haven, CT 06511, USA 2Harvard Forest, Harvard University, Petersham, MA 01366, USA 3Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA 4Department of Geography, Center for Climatic Research, University of Wisconsin-Madison, Madison, WI 53706, USA 5Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA 6Earth and Environmental Science Department, Lehigh University, Bethlehem, PA 18015, USA 7Department of Geography, University of Oregon, Eugene, OR 97403, USA 8Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA 9Division of Earth and Ecosystem Sciences, Desert Research Institute, Las Vegas, NV 89119, USA 10Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA 11School of Biology and Ecology, University of Maine, Orono, ME 04469, USA 12Department of Earth and Environment, Boston University, Boston, MA 02215, USA 13Department of Geology and Geography, West Virginia University, Morgantown, WV 26501, USA 14Department of Geological Sciences, Salem State University, Salem, MA 01970, USA 15Southwest Climate Science Center, US Geological Survey, Tucson, AZ 85719, USA 16Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA 17Department of Geography, University of South Carolina, Columbia, SC 29208, USA 18Department of Geosciences and School of Natural Resources and Environment, University of Arizona, Tucson, AZ 85721, USA 19Biology and Paleo Environment, Lamont-Doherty Earth Observatory, Palisades, NY 10964, USA 20National Snow and Ice Data Center, University of Colorado, Boulder, CO 80309, USA 21Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, USA 22Departments of Biology and Environmental Studies, St. Olaf College, Northfield, MN 55057, USA Correspondence to: Jennifer R. Marlon ([email protected]) Received: 13 October 2016 – Discussion started: 2 November 2016 Revised: 24 June 2017 – Accepted: 2 August 2017 – Published: 13 October 2017 Published by Copernicus Publications on behalf of the European Geosciences Union. 1356 J. R. Marlon et al.: Climatic history of the northeastern US Abstract. Many ecosystem processes that influence Earth vegetation studies or from broad-scale syntheses that inter- system feedbacks – vegetation growth, water and nutrient polate or downscale data to finer scales. cycling, disturbance regimes – are strongly influenced by Temperature changes in the NE US during the late multidecadal- to millennial-scale climate variations that can- Holocene are generally inferred from global, Northern Hemi- not be directly observed. Paleoclimate records provide in- sphere, and North American research that draws on marine formation about these variations, forming the basis of our archives (Marcott et al., 2013), tree rings in adjacent regions understanding and modeling of them. Fossil pollen records (Esper et al., 2002; Mann et al., 2009; Trouet et al., 2013), are abundant in the NE US, but cannot simultaneously pro- and continental-scale pollen-based climate reconstructions vide information about paleoclimate and past vegetation in (Viau et al., 2012; Trouet et al., 2013). Such data show de- a modeling context because this leads to circular logic. If clining temperatures during the past 3000 years (during the pollen data are used to constrain past vegetation changes, “neoglacial”) until about 1700 CE (250 cal yr BP), when the then the remaining paleoclimate archives in the northeast- current regional warming trend began. Sea surface tempera- ern US (NE US) are quite limited. Nonetheless, a grow- ture (SST) reconstructions from marine sediment near Nova ing number of diverse reconstructions have been developed Scotia also indicate consistently cooler-than-present condi- but have not yet been examined together. Here we conduct tions during the past 1500 years (Keigwin et al., 2003). a systematic review, assessment, and comparison of pale- The extent to which broad temperature trends reflect re- otemperature and paleohydrological proxies from the NE US gional, terrestrial climate in the NE US is unclear. Re- for the last 3000 years. Regional temperature reconstruc- sults are contradictory regarding changes during the Me- tions (primarily summer) show a long-term cooling trend dieval Climate Anomaly (MCA; ca. 950–1250 CE; 1000– (1000 BCE–1700 CE) consistent with hemispheric-scale re- 700 cal yr BP) and the Little Ice Age (LIA; ca. 1400– constructions, while hydroclimate data show gradually wet- 1700 CE; 550–250 cal yr BP; Mann et al., 2009). Warming ter conditions through the present day. Multiple proxies sug- during the MCA is not observed in SST reconstructions near gest that a prolonged, widespread drought occurred between Nova Scotia (Keigwin et al., 2003), and ecological stud- 550 and 750 CE. Dry conditions are also evident during the ies have shown complex responses to climate changes dur- Medieval Climate Anomaly, which was warmer and drier ing this interval (Fuller et al., 1998; Umbanhowar, 2004). than the Little Ice Age and drier than today. There is some Vegetation-based climate reconstructions suggest relatively evidence for an acceleration of the longer-term wetting trend high temperatures during the MCA in the deciduous and in the NE US during the past century; coupled with an abrupt hardwood forests of eastern North America about 1300 years shift from decreasing to increasing temperatures in the past ago (Viau et al., 2012) and about 1000 years ago (Trouet century, these changes could have wide-ranging implications et al., 2013), respectively. LIA cooling registers strongly in for species distributions, ecosystem dynamics, and extreme vegetation and fire regimes in both the Midwest and NE (Um- weather events. More work is needed to gather paleoclimate banhowar, 2004; Clifford and Booth, 2013). Vegetation is data in the NE US to make inter-proxy comparisons and to controlled by many factors in addition to climate, however, improve estimates of uncertainty in reconstructions. and would ideally be reserved to evaluate the ecological re- sponses to the climate history rather than used for both cli- mate and ecological reconstruction, especially in a modeling 1 Introduction context. Data reflecting hydroclimatic variability are more abun- Many dimensions of climate – from gradual shifts in temper- dant in the NE US, coming from tree-rings (e.g., Cook and ature and precipitation, to changing seasonal patterns, to ex- Krusic, 2004, 2008; Pederson et al., 2014), lake levels (e.g., treme weather – influence species and ecosystem processes. Shuman et al., 2002), variations in lake chemistry (e.g., Li An ecologically relevant understanding of regional climate et al., 2007), shifts in diatoms (Boeff et al., 2016), and variability thus requires diverse records that overlap in space changes in testate amoeba composition from bog sediments and time. Such an understanding would enable the investiga- (e.g., Booth et al., 2012). Such data show relatively wet con- tion of long-term ecosystem processes, such as succession, ditions in the late versus the mid-Holocene (Digerfeldt et al., large-scale shifts in species composition, and periodic, infre- 1992; Almquist et al., 2001; Shuman et al., 2009) with in- quent disturbances like droughts and flooding, using models creasing effective moisture towards present (Newby et al., or empirical approaches. 2014). Episodic drought and pluvial events, documented by In the northeastern United States (NE US) from the Great a variety of proxies, are superimposed on the gradual trend Lakes to New England, there are few natural archives, such towards increasing moisture (Pederson et al., 2005). The syn- as ice sheets, caves, or corals, that provide long regional cli- chroneity of such events is largely unexplored. mate records. The last deglaciation, however, left thousands To provide a new perspective on regional, terrestrial cli- of lakes and bogs filled with sediments that have recorded mate changes in the NE US (Peterson et al., 2013), we ex- local environmental changes. As a result, the NE US pale- amine local and regional paleoclimate data from the NE US, oclimate has primarily been inferred from local studies and defined here as 100–60◦ E and 38–52◦ N (Fig. 1). Our objec- Clim. Past, 13, 1355–1379, 2017 www.clim-past.net/13/1355/2017/ J. R. Marlon et al.: Climatic history of the northeastern US 1357 tives are to (1) identify the data resources of the region to help constructions. Few proxies can capture multidecadal temper- prioritize and motivate new data collection; (2) improve our ature or moisture variability with high temporal resolution. understanding of regional climate evolution over centuries