Cores from Searsville Lake within Stanford University’s Jasper Ridge Biological Preserve, California, USA, are examined to identify a potential GSSP for the Anthropocene: core JRBP2018-VC01B (944.5 cm-long) and tightly correlated JRBP2018-VC01A (852.5 cm-long). Spanning from 1900 CE ± 3 years to 2018 CE, a secure chronology resolved to the sub-annual level allows detailed exploration of the Holocene-Anthropocene transition. We identify the primary GSSP marker as first appearance of 239,240Pu (372–374 cm) in JRBP2018-VC01B and designate the GSSP depth as the distinct boundary between wet and dry season at 366 cm (6 cm above the first sample containing 239,240Pu) and corresponding to October-December 1948 CE. This is consistent with a lag of 1–2 years between ejection of 239,240Pu into the atmosphere and deposition. Auxiliary markers include: first appearance of 137Cs in 1958; late 20th-century decreases in δ15N; late 20th-century elevation in SCPs, Hg, Pb, and other heavy metals; and changes in abundance and presence of ostracod, algae, rotifer, and protozoan microfossils. Fossil pollen document anthropogenic landscape changes related to logging and agriculture. As part of a major university, the Searsville site has long been used for research and education, serves users locally to internationally, and is protected yet accessible for future studies and communication about the Anthropocene. Plain Word Summary The Global Boundary Stratotype Section and Point (GSSP) for the proposed Anthropocene Series/Epoch is suggested to lie in sediments accumulated over the last ~120 years in Searsville Lake, Woodside, California, USA. The site fulfills all of the ideal criteria for defining and placing a GSSP. In addition, the Searsville site is particularly appropriate to mark the onset of the Anthropocene, because it was anthropogenic activities–the damming of a watershed–that created a geologic record that now preserves the very signals that can be used to recognize the Anthropocene worldwide.

The multi-faceted impacts of the Anthropocene are increasingly modifying natural ecosystems and threatening biodiversity. Protected spaces in and adjacent to urban landscapes may be critical in protecting species in human-modified systems. Can small, protected spaces act as reservoirs for biodiversity across dynamic spatial and temporal gradients of human impact? To address this question, we identified small mammal remains from modern raptor pellets and Holocene archaeological sites along a human modification gradient in the San Francisco Bay Area, CA. We assessed small mammal alpha and beta diversity for both modern and Holocene sites. We tested for significant differences between sites and time bins using permutational multivariate analysis of variance (PERMANOVA) and visualized these differences using non-metric multidimensional scaling (NMDS). We found that alpha diversity decreased with increasing human modification in Anthropocene sites, with no corresponding change between Holocene sites. Additionally, the alpha diversity of modern sites with moderate/high levels of human modification was significantly lower than that of protected modern sites and all Holocene sites, driven by the dominance of human-commensal and disturbance-tolerant species. On the other hand, the small mammal communities from a small, protected area (Jasper Ridge Biological Preserve) retained Holocene levels of alpha diversity. Jasper Ridge has also changed less over time in terms of overall community composition than more modified sites. Despite this, both PERMANOVA and NMDS show that Holocene and Anthropocene communities are significantly distinct regardless of collection site and level of anthropogenic modification. Our results suggest that even relatively small, protected spaces within an urbanized matrix conserve native faunal communities, highlighting their important role in urban conservation.

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The multi-faceted impacts of the Anthropocene are increasingly modifying natural ecosystems and threatening biodiversity. Can small protected spaces conserve small mammal diversity across spatial and temporal scales of human impact? We identified small mammal remains from modern raptor pellets and Holocene archeological sites along a human modification gradient in the San Francisco Bay Area, CA and evaluated alpha and beta diversity across sites and time periods. We found that Shannon diversity, standardized species richness, and evenness decrease across modern sites based on level of human modification, with no corresponding change between Holocene sites. Additionally, the alpha diversity of modern sites with moderate and high levels of human modification was significantly lower than the diversity of modern sites with low levels of human modification as well as all Holocene sites. On the other hand, the small mammal communities from Jasper Ridge Biological Preserve, a small protected area, retain Holocene levels of alpha diversity. Jasper Ridge has also changed less over time in terms of overall community composition (beta diversity) than more modified sites. Despite this, Holocene and Anthropocene communities are distinct regardless of study area. Our results suggest that small mammal communities today are fundamentally different from even a few centuries ago, but that even relatively small protected spaces can partially conserve native faunal communities, highlighting their important role in urban conservation.

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