Investigating the use of microfossils to reconstruct past sea levels from salt-marsh environments in northern Georgia, USA

Lay summary authored by Huixian Chen. Read the full paper here: http://doi.org/10.5334/oq.80

Changes in sea level vary geographically and with time and in response to a variety of processes. These include the melting of land-based ice from ice sheets (Antarctica and Greenland) and glaciers, thermal expansion of the oceans, vertical motions of land (e.g. earthquakes) and by local processes such as the compaction of sediments. Understanding past sea levels provides important background information that is useful for determining how sea levels may change in the future. Our understanding of past sea levels stems from a variety of geological reconstructions that utilize evidence from natural environments (e.g. salt marshes, mangroves and corals). Along the Atlantic coast of North America, salt marshes have provided abundant information of how and why sea levels have changed during the past ~10000 years.

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Salt-marsh environment at Georgetown, northern Georgia, U.S. Atlantic coast. Credit: H. Chen.

The use of salt marshes in providing such information stems from their relationship with tidal levels. Salt-marsh environments typically exist between mean tidal level up to the highest astronomical tide. Further to this, microfossils such as foramnifera living on the surface of the salt marsh may be used to further subdivide the environment into narrower vertical ranges. This is due to different foraminiferal species preference to living conditions including level of salinity and duration of exposure as the tides rise and fall. If we understand and document where these different species live today, we can apply this information to fossil counterparts in sediment cores of known age through methods such as radiocarbon dating and reconstruct how sea levels have changed with greater accuracy.

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Scanning electron microscope images of the most abundant foraminiferal species observed in the salt marshes at Thunderbolt and Georgetown. From left to right: Haplophragmoides wilberti, Miliammina fusca, Ammoastuta inepta. Haplophragmoides wilberti is typically found at higher elevations in the salt marshes. Credit: H. Chen.

In this study, we investigated the surface (top 1cm) distributions of foraminifera from two salt marsh sites, Thunderbolt and Georgetown, in northern Georgia to document where different species live in relation to tidal levels. To do this, we set up multiple surface transects and collected surface sediment for analysis under a microscope. We show that certain species are more prevalent in different areas of the salt-marsh environment and thus have different relationships with tidal levels. We also sampled short (50 cm) sediment cores and analyzed the depth to which living (at the time of collection) foraminifera penetrate down into the subsurface to assess their potential implications for when reconstructing sea level from these environments.

Full paper: Chen, H., Shaw, T.A., Wang, J., Engelhart, S., Nikitina, D., Pilarczyk, J.E., Walker, J., García-Artola, A. and Horton, B.P., 2020. Salt-Marsh Foraminiferal Distributions from Mainland Northern Georgia, USA: An Assessment of Their Viability for Sea-Level Studies. Open Quaternary, 6(1), p.6. DOI: http://doi.org/10.5334/oq.80

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Chronostratigraphy, Site Formation, and Palaeoenvironmental Context of Late Pleistocene and Holocene Occupations at Grassridge Rock Shelter (Eastern Cape, South Africa)

Lay summary authored by Christopher Ames. Read the full paper here: https://doi.org/10.5334/oq.77

The Grassridge archaeological site is a sandstone rock shelter located in the grassland foothills of the Stormberg Mountains in the Eastern Cape of South Africa. Dr Hermanus Opperman of Fort Hare University first excavated the site in 1979. He and his team identified a 1.5 m deep sequence of human occupation at Grassridge, which they divided into two major episodes: a 50–70 cm thick upper portion that is 7,000-6,000 years old, and an underlying 50–80 cm thick portion dated to 36,000 years old at the bottom. This indicates that peopled lived at Grassridge in the lead up to the Last Glacial Maximum (29,000-14,000 years ago), but that it was potentially uninhabited at the height of cold and dry temperatures of the last glacial itself. Located approximately 200 km inland from the Indian Ocean coastline, Grassridge sits at an important environmental intersection between the Drakensberg Mountains to the northeast, the South African coastal zone to the south and southeast, and the interior arid lands of southern Africa to the northwest; the grasslands surrounding Grassridge would thus have been sensitive to past climate change.

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The modern grassland and neighbouring hills that surround Grassridge rock shelter. Photo credit: Lisa Rogers, 2015.

Building on this knowledge, the Grassridge Archaeological and Palaeoenvironmental Project (GAPP) initiated new work at Grassridge in 2014 to reanalyse the stratigraphic sequence and initiate a new excavation programme. In this study, we present the results of our stratigraphic reanalysis, which combines luminescence and radiocarbon dating techniques with sedimentological characterisation and analysis of preserved microbotanical remains to establish the nature of archaeological site formation as well as the palaeoenvironmental contexts of the human occupations. Our work refines the previous excavation results, indicating a history of pulsed human occupation at Grassridge from 43,000-28,000, 13,500-11,600, and 7,300-6,800 years ago. A cool, dry grassland environment is associated with the 43,000-28,000 year old occupation, which transitions to a warmer and wetter grassland environment with more trees—similar to modern conditions—by 7,000 years ago. Moreover, the record at Grassridge confirms the continuation of Middle Stone Age technology at sites in the interior of South Africa until 30,000 years ago or younger, and places Grassridge as one of very few interior sites that preserve occupation from the Younger Dryas (13,000-11,500 years ago). Such a pulsed occupational sequence is characteristic of the regional archaeological record in the high elevation grasslands for the period before, during, and after the Last Glacial Maximum (45,000-5,000 years ago).

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Photo 2: Christopher Ames sampling the lowermost layers of the Grassridge stratigraphic sequence. Photo credit: Benjamin R. Collins,
2018.

This pattern of human occupation seems linked to short distance, rapid environmental changes along an altitudinal gradient in response to rapidly fluctuating palaeoclimatic conditions that occurred across the last glacial to interglacial transition. Only continued joint archaeological and palaeoenvironmental research in the high elevation grasslands and surrounding regions will help evaluate this hypothesis.

Full paper: Ames, CJH, Gliganic, L, Cordova, CE, Boyd, K, Jones, BG, Maher, L and Collins, BR. 2020. Chronostratigraphy, Site Formation, and Palaeoenvironmental Context of Late Pleistocene and Holocene Occupations at Grassridge Rock Shelter (Eastern Cape, South Africa). Open Quaternary, 6: 5, pp. 1–19. DOI: https://doi.org/10.5334/oq.77

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DNA from underwater archaeological sites

Lay summary authored by Lisa Briggs. Read the full paper here: http://doi.org/10.5334/oq.71

The methods used to study ancient DNA have progressed rapidly over the last few decades. As more submerged archaeological sites are discovered and explored, it is possible to apply these new methods and technological advancements in DNA research to recently discovered archaeological material from maritime and underwater sites. Environmental DNA, in particular, has been shown to be particularly important in characterising the human activities that might have taken place at ancient sites, both on land and under the sea. Given these developments, and the heightened awareness of how important it is to characterise the environmental samples taken from archaeological sites, it is necessary to reconsider previously published studies conducted on archaeological material from submerged sites.

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Underwater archaeologist Lisa Briggs recovering artefacts from the Queen Anne’s Revenge shipwreck (Photo credit: W. Welsh)

This paper explores the pitfalls, promise and future directions of ancient DNA research on archaeological material recovered from submerged sites. First, a selection of previously published studies is assessed in light of the new methods and technological advancements that have now been made available to archaeological scientists. Past research conducted on human and animal bones, waterlogged plant remains, and archaeological ceramics is considered. Finding ways to authenticate the DNA recovered as ancient is of paramount importance. Next, the promise that DNA analysis holds for artefacts and environmental samples recovered from underwater sites is explored. Submerged prehistoric settlement sites, ancient shipwrecks, and harbour sites hold particular promise for the application of new methods designed to maximise the recovery of ancient DNA. Finally, the future directions of ancient DNA research on archaeological material from underwater sites are considered. Understanding what DNA is naturally present in the seafloor sediment that accumulates over archaeological sites, what DNA is naturally present in seawater, and how DNA breaks down in the marine environment will greatly enhance our ability to assign an archaeological meaning to DNA discovered on ancient underwater sites.

Full paper: Briggs, L., 2020. Ancient DNA Research in Maritime and Underwater Archaeology: Pitfalls, Promise, and Future Directions. Open Quaternary, 6(1), p.3. DOI: http://doi.org/10.5334/oq.71

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Identifying the Greatest Earthquakes of the Past 2000 Years at the Nehalem River Estuary, Northern Oregon Coast, USA

Lay summary authored by Alan Nelson. Read the full paper here: http://doi.org/10.5334/oq.70

Will the next great earthquake at the Cascadia subduction zone, whose fault dips beneath the coasts of British Columbia, Washington, Oregon, and northern California, be a giant (magnitude 9) like the earthquake and tsunami that killed thousands in Japan in 2011, or the similar Cascadia earthquake in AD 1700? How often do such great earthquakes and their accompanying high tsunamis strike this region? To answer these questions geologists study past great earthquakes beneath coastal wetlands where evidence of them is best preserved.

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Part of the field crew describing earthquake stratigraphy in cores, and taking their GPS locations, in Botts marsh, near the mouth of the Nehalem River, northern Oregon, in July 2009 (Photo: A. Nelson).

Longer fault ruptures produce larger earthquakes, so much effort has gone into determining the length of the Cascadia fault that ruptured during each great earthquake of the past few thousands of years. Usually this has been attempted by radiocarbon dating coastal wetland sediment that records sudden subsidence during earthquakes or their accompanying tsunamis at a series of sites along the coast. But the errors on radiocarbon dating are still too large to distinguish between one giant earthquake rupturing 500-1200 km along the coast, or a series of merely great earthquakes over a few years to a few decades progressively rupturing shorter sections of coast.

At the Nehalem River estuary of northern Oregon we used a more direct method of estimating the magnitude of prehistoric subduction-zone earthquakes—by reconstructing the amount that the coast suddenly dropped down during each great earthquake. The most precise way to measure this sudden subsidence is to study changes in fossil microscopic tidal plants (diatoms) and animals (foraminifera) in tidal sediment at each wetland over thousands of years. Beneath the Nehalem wetlands we identified changes in sediment that suggested three times when the coast suddenly dropped down. Using new statistical methods, combined with information recently gathered by others about how high above low tide modern diatoms and foraminifera typically live, we measured 0.6-1.7 m, 0.3-1.5 m, and 0.6-1.5 m of subsidence during the three earthquakes. Study of fossil diatoms independently confirms similar amounts of subsidence during the two younger earthquakes. Our radiocarbon ages show that the earthquakes occurred about 320, 900, and 1500 years ago.

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Rob Witter (USGS) measures the depths of the upper stratigraphic contacts of two subsided marsh soils, contact A (at 1.1 m on the measuring tape, below his left hand) and contact B (at 0.18 m on the measuring tape, between his knee and ankle), at an outcrop near the mouth of the Nehalem River, northern Oregon, in June 2009. Contact A formed through sudden subsidence of the marsh during the great Cascadia earthquake of 1700 CE. Contact B formed during an earlier great earthquake about 1200-1000 years ago (Photo: A. Nelson).

Although no one can predict the magnitude or time of a future great earthquake, by learning more about past subduction-zone earthquakes, and how their fault ruptures may have varied along the coast, seismologists and geologists hope to forecast the probability and magnitude of a future great earthquake at Cascadia.

Full paper: Nelson, A.R., Hawkes, A.D., Sawai, Y., Engelhart, S.E., Witter, R., Grant-Walter, W.C., Bradley, L.-A., Dura, T., Cahill, N. and Horton, B., 2020. Identifying the Greatest Earthquakes of the Past 2000 Years at the Nehalem River Estuary, Northern Oregon Coast, USA. Open Quaternary, 6(1), p.2. DOI: http://doi.org/10.5334/oq.70

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Rock-boring organisms tell us about sea-level fluctuations in a warmer world

Lay summary authored by Michaela Falkenroth. Find the full paper here: http://doi.org/10.5334/oq.72

The Last Interglacial, 130.000 until 115.000 years ago, was the last time global mean temperatures and global sea-level were higher than today. This has put the period onto the agenda of scientists, who are asked to provide communities with scenarios of coastal evolution in a warming world. Researchers currently conduct a global database of areas, where remains of last interglacial shorelines still present today.

One of these areas is the coastline of Oman, that borders the western Indian Ocean. While the Sultanate`s coastlines are for the most part preserved in their natural state without any anthropogenic influence, a true rarity among the coastlines of the world, their sea-level history is still understudied.

Last Interglacial Paleoshoreline with notch (left) and beachrock (right) in Sur

Last Interglacial Paleoshoreline with notch (left) and beachrock (right) in Sur (Photo: M. Falkenroth).

With this work we wish to lay the ground for research on last interglacial shorelines in Oman. Our example is a very well preserved tidal notch at Sur Lagoon that is located 3.93 m above recent mean sea level. Tidal notches are carved into rocky shorelines by wave action and organisms that bore into hard substrates. These organisms can be clams, sponges or worms that create cavities in a rock-surface by chemical dissolution and mechanical action. The cavities function as shelter for the animal or are a side effect of its feeding behaviour.

A tidal notch is an indicator for sea-level as its deepest point lies at mean sea-level while its floor and roof represent the tidal range. Because the process of notch-formation is rather slow, they form in periods during which sea-level remained stable. This also means that the notch itself will not significantly change if mean sea-level rises or falls for a short period of time.

Rocksurface with Lithiphaga borings

Rocksurface with Lithiphaga borings (Photo: M. Falkenroth).

The organisms living within the notch however, will change their behaviour almost instantaneously, as their habitat is restricted to a certain bathymetry. The common boring clam Lithophaga needs to be permanently submerged. When sea-level falls, Lithophaga will abandon all newly exposed surfaces and if sea-level rises the clams will penetrate the newly submerged rocksurface within a couple of years.

This can lead to a mismatch between the shape of a tidal notch and the distribution of organisms within it, as they act on different timescales. The tidal notch in Sur shows Lithophaga borings above the notch roof, which are interpreted as remains of a short term sea-level rise subsequent to notch-formation and tell a story of last interglacial sea-level variability.

Full paper: Falkenroth, M., Adolphs, S., Cahnbley, M., Bagci, H., Kázmér, M., Mechernich, S. and Hoffmann, G., 2020. Biological Indicators Reveal Small-Scale Sea-Level Variability During MIS 5e (Sur, Sultanate of Oman). Open Quaternary, 6(1), p.1. DOI: http://doi.org/10.5334/oq.72

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“Animals and people in the Netherlands’ past”: >50 years of archaeozoology in the Netherlands

Lay summary authored by Canan Çakırlar and Youri van den Hurk. Read the full paper here: http://doi.org/10.5334/oq.61

It has been more than 50 years since the late Prof. Anneke T. Clason published her PhD thesis, Animal and Man in Holland’s Past (Clason 1967), based on animal bone remains excavated at sites in the Province of Holland in the Netherlands. Subsequently, Clason became the leading archaeozoologists (also called a zooarchaeologist – a specialist expert who analyses animal remains from archaeological sites) in the Netherlands, as well as its international face. Since the late 1960’s, her colleagues and students have built a strong tradition of archaeozoology in the Netherlands, producing, interpreting and publishing an enormous amount of data.

However, most archaeozoological data remain difficult to access and/or are scattered in grey literature in Dutch. Syntheses are scarce. The scarcity of overviews hinders efforts to train, strategize, and internationalize this field of study in the Netherlands. Inspired by the 50th anniversary of Clason’s career launch, we wrote this review article to provide an accessible introduction for beginners in and outsiders to Dutch archaeozoology.

Extinctions and introductions Netherlands aa

Figure 1: Overview of introductions and extinctions of some mammal and bird species in the Netherlands during the Holocene. BC and AD dates are calendar years (calibrated dates).

As part of this synthesis, we discuss twelve themes that have received the most attention from Dutch archaeozoologists and their predecessors over the past 50 years, bringing together a thorough and extensive overview of the archaeozoology of the Netherlands from the Palaeolithic to the Middle Ages. The themes vary from regional (e.g. archaeozoology of terps (artificial dwelling mounds in the northern part of the Netherlands)) to chronological (e.g. archaeozoology of the Bronze and Iron Ages) to overarching overviews (e.g. extinctions and invasions; see figure 1).

Each thematic section draws data from the most thoroughly studied (e.g. medieval site of Dorestad), interesting and/or best-known sites and assemblages (e.g. Swifterbant culture sites), and offers suggestions for future research directions (e.g. the beginnings of animal domestication and breed improvement). We display the wealth of archaeozoological information, the impact it can have on our understanding of human-animal interactions in the past, and how we can use this data to inform conservation.

References
Clason, A. 1967. Animal and man in Holland’s past: an investigation of the animal world surrounding man in prehistoric and early historic times in the provinces of North and South Holland. Unpublished thesis (PhD), Rijksuniversiteit Groningen.

The full paper in Open Quaternary: Çakirlar, C., van den Hurk, Y., van der Jagt, I., van Amerongen, Y., Bakker, J., Breider, R., van Dijk, J., Esser, K., Groot, M., de Jong, T., Kootker, L., Steenhuisen, F., Zeiler, J., van Kolfschoten, T., Prummel, W. and Lauwerier, R., 2019. Animals and People in the Netherlands’ Past: >50 Years of Archaeozoology in the Netherlands. Open Quaternary, 5(1), p.13. DOI: http://doi.org/10.5334/oq.61

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A multi-proxy reconstruction of environmental change in the vicinity of the North Bay outlet of pro-glacial Lake Algonquin

Lay summary authored by Ryan Rabett. Read the full article at: http://doi.org/10.5334/oq.54

At the end of the last Ice Age large frigid lakes formed in the Great Lakes region of North America in front of the retreating Laurentide ice‐sheet. Subject to the effects of periodic meltwater surges through the lake system and by the rebound of the land itself once the great weight of the ice had gone, these lakes underwent repeated changes in shape, depth and drainage over comparatively short periods (with individual phases tending to last hundreds rather than thousands of years). Despite such changeable conditions the archaeological evidence that survives from this time suggests that their shorelines and the surrounding environment were capable of sustaining forays by Late Palaeoindian groups venturing into this new landscape from further to the south, though information is scant.

Balsam Creek kettle lake basin

Balsam Creek kettle lake basin (Photo: R. Rabett).

For this project we aimed to produce a new environmental record for northeast Ontario, an area that featured centrally in the late drainage history of one such lake: Lake Algonquin. At its height, 13‐11,000 years ago, Algonquin was the largest lake in the Great Lakes Basin, filling the area of today’s Huron and Michigan Great Lakes as well as a swathe of adjacent lands. Following reconnaissance by the senior project author (PK), we extracted and analysed a core from a small lake in a suitable location c. 34 km north‐east of the city of North Bay, Ontario near the hamlet of Balsam Creek.

Coring in the Balsam Creek kettle lake

Coring in the Balsam Creek kettle lake (Photo: T. Rabett).

The environmental history preserved in the bed of the lake begins c. 10,500 years ago, following one of the final phases in Algonquin’s late evolution, and when the local landscape had become only recently ice‐free. From there on the core extends through time up to the last few hundred years. Among our results we identified two early intervals when deteriorating climate conditions significantly affected vegetation around the lake. Interestingly, both coincided with peaks in volcanic ash (attributed to eruptions in Oregon) also identified in the core, suggesting a possible association. Outside of these times, however, the character of the local forest did not change significantly, indicating that this and other small similarly enclosed lake basins may have been less susceptible to resource disturbance affecting the wider landscape. Given the scarcity of well‐preserved Late Palaeoindian sites in this part of Ontario, such locales could represent a profitable focus for future archaeological investigation of the first human pioneers to enter the Northlands.

Trekking to the Balsam Creek kettle lake

Trekking to the Balsam Creek kettle lake (Photo: T. Rabett).

Rabett, R.J., Pryor, A.J.E., Simpson, D.J., Farr, L.R., Pyne-O’Donnell, S., Blaauw, M., Crowhurst, S., Mulligan, R.P.M., Hunt, C.O., Stevens, R., Fiacconi, M., Beresford-Jones, D. and Karrow, P.F., 2019. A Multi-Proxy Reconstruction of Environmental Change in the Vicinity of the North Bay Outlet of Pro-Glacial Lake Algonquin. Open Quaternary, 5(1), p.12. DOI: http://doi.org/10.5334/oq.54

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