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Palaeoenvironmental data indicate late quaternary anthropogenic impacts on vegetation and landscapes in Mzimba, northern Malawi

January 2024
Frontiers in Environmental Archaeology 2

DOI:10.3389/fearc.2023.1250871

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Authors:

Sarah Ivory

Pennsylvania State University

Jago Jonathan Birk

University of Göttingen

Jeong-Heon Choi

Korea Basic Science Institute

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Landscapes are formed by long-term interactions between the underlying geology and climatic, edaphic and biotic factors, including human activity. The Kasitu Valley in the Mzimba District of northern Malawi includes the Kasitu River and its adjacent floodplains and uplands, and it has been a location of sustained human occupation since at least 16 thousand years ago (ka) based on archaeological excavations from rockshelters. We trace the changing ecology and geomorphology of the region through soil stable isotopes (δ ¹³ C, δ ¹⁵ N), microcharcoal and fossil pollen analysed from alluvial terraces dated by Optically Stimulated Luminescence, and wetland auger cores and archaeological sites dated by radiocarbon. Our results suggest that the region was primarily covered in mosaic forest at ca. 22.5 ka. Middle and Late Holocene samples (6.0–0.5 ka) show an increasingly open, herbaceous landscape over time with an inflection toward more abundant C4 vegetation after 2 ka. Significant upland erosion and terrace formation is also evidenced since 2 ka alongside high concentrations of microcharcoal, suggesting more intensive use of fire. Faecal biomarkers simultaneously indicate higher numbers of humans living adjacent to the archaeological site of Hora 1, which may be indicative of an overall population increase associated with the arrival of Iron Age agropastoralists. More recently, the introduction of exogenous commercial taxa such as Pinus sp. are correlated with regional afforestation in our proxy record. These results show increasing stepwise human impacts on the local environment, with deforestation and maintenance of open landscapes correlated with the regional introduction and intensification of agriculture during the Late Holocene.

FIGURE Schematic profiles of wetland auger tests from the Mzimba region, Malawi showing sedimentation, soil development, and the locations where samples were taken from the cores. AUU and AUU were extracted in sequences using a percussion auger to access deeper aspects of the landform until refusal occurred. Sediment and soil classification schemes follow the USDA standards as outlined in Schoeneberger et al. ().

…

FIGURE Ratios of the n-alkanes CCC/CCC and CCC/CCC on the left, with high values showing a higher input of biomass of broadleaf trees and low values a higher input of grasses and other herbaceous plants. Ratio of (coprostanol + epi-coprostanol)/cholestanol with high values characteristic for inputs of omnivorous faeces (likely from humans) from AUU, Mzimba region, Malawi.

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TYPE Original Research

PUBLISHED 05 January 2024

DOI 10.3389/fearc.2023.1250871

OPEN ACCESS

EDITED BY

Sjoerd Kluiving,

VU Amsterdam, Netherlands

REVIEWED BY

David Kaniewski,

Université Toulouse III - Paul Sabatier, France

Harald Stollhofen,

Friedrich-Alexander-Universität

Erlangen-Nürnberg, Germany

*CORRESPONDENCE

David K. Wright

david.wright@iakh.uio.no

Jessica C. Thompson

jessica.thompson@yale.edu

RECEIVED 30 June 2023

ACCEPTED 05 December 2023

PUBLISHED 05 January 2024

CITATION

Wright DK, Ivory SJ, Birk JJ, Choi J-H, Davies B,

Fiedler S, Davis J, Kaliba P and Thompson JC

(2024) Palaeoenvironmental data indicate late

quaternary anthropogenic impacts on

vegetation and landscapes in Mzimba, northern

Malawi. Front. Environ. Archaeol. 2:1250871.

doi: 10.3389/fearc.2023.1250871

Davis, Kaliba and Thompson. This is an

open-access article distributed under the terms

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original author(s) and the copyright owner(s)

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does not comply with these terms.

Palaeoenvironmental data

indicate late quaternary

anthropogenic impacts on

vegetation and landscapes in

Mzimba, northern Malawi

David K. Wright 1*, Sarah J. Ivory 2, Jago J. Birk 3,4,

Jeong-Heon Choi 5, Benjamin Davies 6, Sabine Fiedler 3,

Jacob Davis7, Potiphar Kaliba 8and

Jessica C. Thompson 9,10,11*

1Department of Archaeology, Conservation, and History, University of Oslo, Oslo, Norway, 2Department

of Geosciences, Earth and Environmental Systems Institute (EESI), Penn State University, University Park,

PA, United States, 3Institute of Geography, Johannes Gutenberg-University, Mainz, Germany, 4Institute

of Geography, Georg-August-Universität Göttingen, Göttingen, Germany, 5Research Center for

Geochronology and Isotope Analysis, Korea Basic Science Institute, Ochang, Chungbuk, Republic of

Korea, 6Environmental Studies Program, Tufts University, Medford, MA, United States, 7Yale University,

New Haven, CT, United States, 8Malawi Department of Museums and Monuments, Lilongwe, Malawi,

9Department of Anthropology, Yale University, New Haven, CT, United States, 10Yale Peabody Museum,

Yale University, New Haven, CT, United States, 11Institute of Human Origins, School of Human Evolution

and Social Change, Arizona State University, Tempe, AZ, United States

Landscapes are formed by long-term interactions between the underlying geology

and climatic, edaphic and biotic factors, including human activity. The Kasitu Valley

in the Mzimba District of northern Malawi includes the Kasitu River and its adjacent

ﬂoodplains and uplands, and it has been a location of sustained human occupation

since at least 16 thousand years ago (ka) based on archaeological excavations

from rockshelters. We trace the changing ecology and geomorphology of the

region through soil stable isotopes (δ13C, δ15N), microcharcoal and fossil pollen

analysed from alluvial terraces dated by Optically Stimulated Luminescence, and

wetland auger cores and archaeological sites dated by radiocarbon. Our results

suggest that the region was primarily covered in mosaic forest at ca. 22.5 ka. Middle

and Late Holocene samples (6.0–0.5 ka) show an increasingly open, herbaceous

landscape over time with an inﬂection toward more abundant C4 vegetation after

2 ka. Signiﬁcant upland erosion and terrace formation is also evidenced since 2

ka alongside high concentrations of microcharcoal, suggesting more intensive

use of ﬁre. Faecal biomarkers simultaneously indicate higher numbers of humans

living adjacent to the archaeological site of Hora 1, which may be indicative of an

overall population increase associated with the arrival of Iron Age agropastoralists.

More recently, the introduction of exogenous commercial taxa such as Pinus sp.

are correlated with regional aorestation in our proxy record. These results show

increasing stepwise human impacts on the local environment, with deforestation

and maintenance of open landscapes correlated with the regional introduction

and intensiﬁcation of agriculture during the Late Holocene.

KEYWORDS

African Iron Age, erosion, stable isotopes of carbon and nitrogen, organic biomarkers,

pollen analysis, archaeoecology, Optically Stimulated Luminescence, human landscape

interactions

Frontiers in Environmental Archaeology 01 frontiersin.org

Wright et al. 10.3389/fearc.2023.1250871

1 Introduction

There is no question that humans have radically changed

the complexion of all spheres of Earth’s environment. Many

scientists have proposed that the signiﬁcant, irreversible eﬀects

of anthropogenesis (human-induced landscape formation) began

with the introduction and adoption of formal agricultural

techniques in the Holocene (Ellis, 2011;Ruddiman, 2013;

Ruddiman et al., 2015). However, there is growing awareness

that hunter-gatherers exert signiﬁcant impacts on ecological

systems, and therefore anthropogenesis may extend deeper into

the Pleistocene (Boivin, 2016;Roberts et al., 2017;Boivin and

Crowther, 2021;Snitker, 2022). In particular, the use of ﬁre (Bird,

2008;Pinter et al., 2011) and extirpation of megafauna (Braje

and Erlandson, 2013;van Der Kaars et al., 2017) altered the

natural environment in favor of one that was produced by and

for human subsistence pursuits. Land use in northern Malawi, as

in other rural landscapes in Africa, is predominately agricultural

and the ecology of the region has been adapted for that purpose.

However, there are many intermediary steps between an ecological

system fully adapted to hunting and gathering to one that is fully

adapted to farming. Here, we adopt a landscape archaeological

approach to study the ecological impacts of climate and human

activity on vegetation structure and geomorphology from the

Late Pleistocene to Late Holocene of a perennial river valley

system in northern Malawi, southern-central Africa. We examine

the evolving relationships between human land use and climatic

conditions at diﬀerent points in time and evidence for ecological

impacts such as erosion and vegetation change.

The East African Rift System (EARS) and adjacent areas

have long been known to be “hotspots” of human occupation

because of the topographic variability resulting in precipitation

and temperature gradients that are ideal for species adapted for

environmental variability such as our own (Potts, 1998). After the

emergence of Homo sapiens, genetic and linguistic evidence show

that as the continent with the longest record of human occupation,

it is also the most genetically and linguistically diverse (Beltrame

et al., 2016;Vicente and Schlebusch, 2020;Fan, 2023). These long

legacies of human innovation, migration, and information sharing

have resulted in a variety of landscape management systems that

can be examined in a range of environmental settings. Today,

this is evidenced by the myriad subsistence practices that are

documented across the continent (Garrity et al., 2012), but the

roots of these systems extend deep into prehistory and have

signiﬁcantly impacted the formation of present-day ecological

systems (Stephens, 2019;Ellis, 2021;Wright, 2022).

Signiﬁcant questions remain about when and at what scale

anthropogenic eﬀects manifested as permanent components of

ecosystem functionality in many parts of the world. In northern

Malawi, archaeological, geomorphic, and lake core data show that

within the last ∼85 ka, vegetation changes that followed climate-

driven variation were modiﬁed by the eﬀects of anthropogenic

burning (Thompson et al., 2021). By the terminal Pleistocene,

human-inﬂuenced landscapes and environments were therefore

already well-established through the behaviour of hunter-gatherers,

who were then displaced by food producers that migrated into the

region by at least 1.7 ka (Juwayeyi, 2011). Along with agriculture

and pastoralism, extractive technologies such as pottery production

and ironworking would have represented very diﬀerent modes of

land use, and potentially diﬀerent scales and forms of impacts

on environments. Additional migrations into Malawi, documented

through archaeology, oral history, and written history, continued

throughout the last ca. 0.5 thousand years (kyr) and resulted in new

patterns of land use and ecological succession (Thompson, 1981;

Juwayeyi, 2020). Increasingly from the mid-1700s, the inﬂuence of

external economic interests aﬀected patterns of human movement,

trade, and resource extraction, particularly ivory and enslaved

people (Morris, 2006;Dussubieux et al., 2023). Today, the country

is one of the most populous in Africa, and ∼56% of the total

land is used for agriculture (Li et al., 2017). However, there is

little information about the point at which farming technologies

transformed the environment through erosion, ecological turnover,

and/or establishment of burning ecologies.

Here, we present the results of a combined archaeological-

palaeoecological research program from north-central Malawi in

which there are human burials dating to at least 16 thousand

years ago (ka) (Lipson et al., 2022), although direct evidence for

human habitation outside the rockshelters is nearly absent. We

seek to identify evidence for ecological “tipping points” (Lenton,

2013;Tylianakis and Coux, 2014;Brovkin et al., 2021) in the

past through the study of micro-scale palaeoecological indicators

from the landscapes surrounding these archaeological sites. The

application of palaeoecological techniques from upland swamps

(called dambos locally) has opened new possibilities to understand

landscape formation processes dating to the same periods of

human occupation. By coring, recovering, dating and analysing

faecal biomarkers, pollen and light stable isotopes from soil, and

studying geomorphic processes on the riverbanks from locations

surrounding the rockshelters, we provide insights about the degree

of anthropic inﬂuence on the formation of the landscape over time.

2 Background to the research area

The study region (Figure 1) is located in the humid sub-

tropical climate (Cwa) of south-central Africa (Kottek et al.,

2006). The Mzimba District lies on the southern end of the

Intertropical Convergence Zone, a pressure meridian extending

across the tropics that migrates on an annual basis following the

zone of maximum insolation. This creates a strongly bimodal

precipitation gradient in this region with high precipitation

during the austral summer (December–March) and almost no

precipitation during the austral winter (June–September). The

annual average precipitation from 1961 to 1990 was 903 mm/yr

with an austral winter precipitation averaging <1 mm/month and

an austral summer precipitation ranging between 164 and 230

mm/month (NOAA, 2022).

The Lake Malawi region has been subject to climate ﬂuctuations

in concert with orbital changes throughout the Quaternary,

however, as most of the palaeoenvironmental information comes

from drill cores in Lake Malawi, the catchment scale landscape

response is not well known. Precipitation reconstructions are

regional and suggest climate patterns were driven by a combination

of Northern Hemisphere high latitude forcing and local insolation

forcing from the late Pleistocene to Holocene (Konecky et al., 2011;

Chevalier and Chase, 2015). Landscape formation was, however,

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Wright et al. 10.3389/fearc.2023.1250871

FIGURE 1

Location of the study area in northern Malawi. Land cover categories derived from the Global Land Cover Characterization (GLCC) version 1 (USGS,

2018a). Hillshade background produced from GTOPO30 global 1-km digital raster data (USGS, 2018b).

patchy in nature across southern-central Africa. For example, an

εNd study of clays from the Zambezi River, which lies over 500 km

south of the Mzimba region, shows relatively high discharge during

MIS2 relative to MIS3; however, the lowest discharge in the record

occurs between 15 and 7 ka (van der Lubbe et al., 2016). On

the other hand, studies of lignin phenols, n-alkanes, and pollen

from a lake core in the northern Lake Malawi basin indicate tree

cover from 17 to 13.6 ka and 7.7 to 2 ka, suggesting overall wetter

conditions than in the intervening time periods (Castañeda et al.,

2009;Ivory et al., 2012). These data correspond to stable isotope

values analysed from herbivores from the archaeological site of

Makwe, eastern Zambia, which show C3 (woodland) conditions

throughout the Holocene followed by C4 (grassy) conditions after

2 ka (Robinson and Rowan, 2017). Similarly, δDn-C31 alkanes

from the Zambezi catchment (Schefuß et al., 2011) indicate a

regional climatic condition of drier, more open landscapes in the

Late Holocene compared to the Middle Holocene. Overall, growing

impacts of deforestation and increased warming are reﬂected in

the organic geochemistry of Lake Malawi over the last 700 years

(Castañeda et al., 2011), which accords with regional studies such

as in the Zambezi catchment, demonstrating the persistence of

more open grassland settings, likely as a result of human land use

and ﬁre patterns (Burrough and Willis, 2015). Overall, the patterns

observed in the proxy record are spatially heterogeneous but show

increasing inﬂuences of humans over time that overprint orbitally

driven climate cycles.

The research area is situated in the Irumide terrane to the west

of the EARS in uplands comprised of Precambrian to Palaeozoic

biotite and hornblende rich schists and gneisses to the east, grading

to unconsolidated Tertiary and younger sediments to the west

and into Zambia (Hopkins, 1973). Residual alluvial and colluvial

deposits are found at distal margins of talus slopes that form in

response to normal faulting and uplift in the valleys or inselberg

outcrops. Sand-rich ﬂuvial terraces draining uplands primarily to

the east are found along the margins of the Kasitu River and

subordinate drainages and incise older, residual landforms.

Soils in the study area are primarily geogenic and are classiﬁed

in the Food and Agriculture Organization’s World Reference Base

for Soil Resources as Rhodic Lixisols and Lixic Ferralsols with

the river valley alluvial classiﬁed as Ferralic Endogleyic Cambisols

(IUSS Working Group WRB, 2015). Lixisols [sometimes called

“latosols” and equivalent to Ustalfs in the United States Department

of Agriculture (USDA) soil taxonomy; Soil Survey Staﬀ, 1999]

generally formed under wetter conditions than present and have

been subject to clay elluviation via translocation of ﬁne mineral

fraction from the upper to lower aspect of the solum (Ebelhar

et al., 2008). Ferralsols (sometimes called “laterites” or “latosols”

and equivalent to Oxisols in the USDA soil taxonomy) have high

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Wright et al. 10.3389/fearc.2023.1250871

amounts of kaolinite and iron, aluminum and titanium oxides (Paz

et al., 2008). Cambisols (Inceptisols in the USDA soil taxonomy)

are poorly developed soils, which, in this setting, have indistinct

reddish subsoils forming in alluvium (Chesworth et al., 2008).

Overall, the project area is located in a region with patchy suitability

for agricultural production, with river valleys hosting the units of

land requiring the least intensive dry season eﬀorts at maintaining

crops (Li et al., 2017).

The vegetation of the study area is marked by woodlands,

grasslands and seasonally ﬂooded grassland swales called dambos

characteristic of the Sudano-Zambezian region (Werger and

Coetzee, 1978). Dambos are typically vegetated with Loudetia

simplex, which ﬂourishes on the clayey soils that build up with

annual inundation (Kindt et al., 2014). Surrounding dambos,

the natural vegetation of the Mzimba District is comprised of

Brachystegia and Julbernardia miombo woodland with grassier

occurrences on the Mbelwa Plains to the west (Jackson, 1968).

Miombo woodlands are distributed extensively across southern

Africa where long dry seasons predominate and include mixed

closed and open canopy settings with shallow soils (Frost, 1996).

Pollen traps set in the early 1980s on the Nyika Plateau, located

∼100 km north of the study region, collected high abundances

of herbaceous pollen taxa including Poaceae, Cyperaceae and

Apiaceae along with arboreal pollen taxa such as Olea,Juniperus,

and Podocarpus, indicating the modern conﬁguration of high-

elevation grasslands above ∼2000 m above mean sea le vel (AMSL)

with pockets of forest retained between hillslopes (Meadows,

1984b). Pollen from peat cores in dambos in the Nyika at the bases

of these slopes show that these characteristics were a feature of the

region for at least the last 5 kyr, and potentially throughout the

Holocene (Meadows, 1984a).

The study area of the Kasitu Valley and adjacent Viphya

Uplands ranges from ∼1350 to 1750 m AMSL, and as is

characteristic of this physiographic region, there is a strong mix

of trees (most of which follow a C3 photosynthetic pathway)

and grasses (C4 photosynthetic pathway). The degree of openness

is inﬂuenced by overall rainfall, its seasonal distribution, soil

characteristics, and slope aspect (north-facing slopes in the

southern hemisphere receive more sunlight, promoting vegetation

that can tolerate warmer and/or more xeric conditions). Once more

open woodlands are established, they may be maintained through

soil compaction that reduces water inﬁltration and promotes

erosion, creating vegetation-landscape feedback loops (Campbell

et al., 1995).

Fire also plays an important role in these landscapes

of maintaining open vegetation structure. A local study of

Butyrospermum paradoxum suggests that the evolutionary

pathways to ﬁre-dependent germination in the region extend deep

into the past and may indicate a long-term relationship between

anthropogenic burning and vegetation patterning (Jackson,

1974). Currently, the oldest evidence for human intervention

in vegetation character comes from charcoal and pollen records

from two deep cores in Lake Malawi, MAL05-2A (near Karonga)

and MAL05-1B/1C (near Nkhata Bay), corresponding to changes

observed in adjacent archaeological sites entrained within alluvial

fans that formed within the last ∼100 kyr (Thompson et al.,

2021). By ca. 85 ka, overall wetter conditions in the basin were

no longer associated with extensive Afromontane forests, and

ﬁre-tolerant taxa had become more common. However, there is

less information about local-scale connections between climate,

environment, and human behaviour. The terminal Pleistocene

and Holocene are not well-studied in the MAL05-1B/1C core that

produced records of pollen and charcoal extending beyond 600 ka

(Ivory, 2018), but the M96 core from Lake Masoko in southern

Tanzania, −300 km northwest of our study area (Garcin et al.,

2007), and the MAL05-2A core from Lake Malawi, ∼150 km to the

northeast (Ivory et al., 2012), oﬀer basin-scale information about

changes in vegetation in northern Malawi during this time. Both

cores show an increased seasonal dry forest in the Holocene, with a

transition between ca. 14.5 and 11.8 ka toward higher proportions

of grassy ground cover at the expense of Afro-montane tree

taxa. This is supported by an increase in herbaceous pollen at a

comparable depth in the M86-18P core from near Nkhata Bay,

∼70 km east of our study area (DeBusk and George, 1998).

Charcoal records from Lake Malawi are not sampled at a ﬁne

enough resolution to examine changes in burning regime within

the last ca. 18 kyr, the period covering the transition out of the

Last Glacial Maximum (LGM), through the terminal Pleistocene,

and across the Holocene. Charcoal from Lake Masoko, in southern

Tanzania, shows increases in regional ﬁre emissions starting around

ca. 1.8 ka, with more input from local ﬁres by ca. 1.5 ka (Thevenon

et al., 2003). Between 1.1 – 0.6 ka, a reduction in evidence for ﬁre

activity corresponds to a reduction in available fuel load, resulting

in vegetation that has potentially been shaped through a series of

interactions between climate and human activity (Vincens et al.,

2003).

Here, we provide local-scale datasets derived from the late

Quaternary terraces of the Kasitu River and a series of dambos

that provide environmental context for archaeological sites that

span over 16 kyr. In the Kasitu Valley today, vegetation is

strongly inﬂuenced by economic activities such as agriculture

and charcoal production. By providing ﬁnely resolved local

records of environmental and geomorphic change, we demonstrate

the antiquity, scale, and consequences of climate and human

impacts across four key transitions: (1) LGM to terminal

Pleistocene; (2) terminal Pleistocene to Holocene; (3) foraging

to food production and (4) globalisation of commerce with the

African interior.

3 Project description and data

collection

3.1 Malawi Ancient Lifeways and Peoples

Project

The Malawi Ancient Lifeways and Peoples Project (MALAPP)

began in 2016 with survey and new excavations at Hora 1

rockshelter (HOR-1, 1470m AMSL), where two adult human

burials were recovered in 1950 (Clark, 1956), and directly dated

to ca. 8–9 ka (Skoglund et al., 2017;Lipson et al., 2022).

MALAPP excavations in 2019 recovered two infant burials, dated

stratigraphically to ca. 14–16 ka (Lipson et al., 2022). All four

individuals produced ancient DNA that contributed to discovery

of ancient population structure that emerged at the end of the

terminal Pleistocene (Skoglund et al., 2017;Lipson et al., 2022).

Frontiers in Environmental Archaeology 04 frontiersin.org

Wright et al. 10.3389/fearc.2023.1250871

The total sample of ancient individuals from northern Malawi (n

=8) further show that the spread of farmers with western African

ancestry into the region during the Late Holocene resulted in

genetic replacement of local hunter-gatherer populations (Lipson

et al., 2022). The broad context of human occupation in the

terminal Pleistocene and Holocene are primarily found at the

sites of HOR-1 (ca. >16–8 ka), and three other sites excavated

by MALAPP: Hora 5 (HOR-5, 1503 m AMSL, ca. 5–2.6 ka),

Kadawonda 1 (KAD-1, 1709 m AMSL, ca. 3.8–1 ka) and Mazinga

1 (MAZ-1, 1401 m AMSL, ca. >9.5–0 ka) (Figure 2). All sites have a

small amount of historical and Iron Age material in the uppermost

∼10 cm (e.g., Miller et al., 2021;Dussubieux et al., 2023).

MALAPP has prioritised the recovery of ecological datasets

to better connect human-environmental processes, but on-site

records represent discontinuous blocks of time. To that end,

reconnaissance for more continuous and ﬁne-grained sequences of

environmental change has been conducted in parallel to the on-

site archaeological work since 2017. This work involved collection

of soils and sediments from speciﬁc geomorphic contexts for the

purpose of recovering and identifying stable isotopes of carbon and

nitrogen, coprostanol (an organic molecule associated primarily

with human faeces) and fossil pollen. We used two primary

methods: (1) scraping, drawing proﬁles and collecting sediments

in 100 mL Whirlpaks from excavated or exposed test units on

Kasitu River terraces; and (2) utilising a percussion auger to

collect polythene cores in 30-cm increments from ﬂoodplain and

dambo (upland wetland) environments. Following the collection

of percussion augers, the cores were opened, documented and

sampled at the ﬁeld laboratory of the M’Mbelwa Farm Institute near

Lunjika Mission, Malawi. Sediments were then air dried prior to

sealing and exporting to the United States, Norway and Germany

for analysis.

Locations for auger testing were selected based on the

identiﬁcation of upland swales that were feasible to test and

provided spatial context to understand ecological conditions

at diﬀerent distances to known archaeological rockshelter

sites. We documented four sedimentologic proﬁles (sampling

three redundantly in 2017 and 2018) and extracted seven

percussion augers. Of the percussion auger samples, four were

sampled for environmental proxies (fossil pollen, soil stable

isotopes, biomarkers). An eighth percussion auger (AU8) was

attempted, but the bucket attachment broke, after which a

sediment pit (Pit 8) was excavated to retrieve samples for

environmental reconstruction.

Locations of ecological proxy collection points were situated in

two primary contexts: (1) the Kasitu River valley from sand-rich

alluvial terraces dating from 34.6 to 0.5 ka. (2) Three dambo upland

swale locations with clay-dominant sediments at diﬀerent distances

to the archaeological site of HOR-1. AU7 is situated on the eastern

slope of Mount Hora (700 m from the site under excavation).

AU8 (Pit 8) is located 4km west of Mount Hora in an adjacent

drainage catchment to HOR-1. This unit is capped by ∼50 cm of

coarse sands, under which clay-rich dambo sediments predominate

with the basal 20 cm comprised of sandy loam alluvium. AU3 is

located 11.5 km northwest of Mount Hora in a catchment that is not

directly connected or adjacent to HOR-1. The purpose of the latter

set of samples will be to evaluate land cover changes associated with

diﬀerent scales of human settlement.

3.2 Analytical methods

3.2.1 Geomorphology, pedology, and

sedimentology

Depositional context was ﬁrst assessed from satellite images,

followed by site visits and documentation of exposed or extracted

proﬁles. In the case of terraces along the Kasitu and tributaries,

sediment grain sizes and sedimentary structures were noted

to infer past ﬂuvial depositional patterns. Soil formation was

documented to infer periods of landform stability and weathering

features (e.g., redox processes, laterisation) that reﬂect ground

cover and hydrologic conditions. Complete descriptions of the

sediment and soil characteristics of the terrace proﬁles and

auger cores sensu Schoeneberger et al. (2012) are found in the

Supplementary material.

For auger tests, sediments and soils were documented in

the ﬁeld lab after splitting the 30-cm PVC extraction sleeves

lengthwise into two halves, undertaking careful documentation

of the sediment grain sizes and soil formation features using a

hand lens and dental picks, and removing 50–100 g samples from

geologically representative locations within the cores believed to

be able to reﬂect changing environmental conditions over the

depositional period. Once the cores were split on the laboratory

table, samples for stable isotope and organic biomarker analyses

were arbitrarily (but systematically) extracted in 2–3-cm thick

units from the left side of the core. Between samples, utensils

were scrubbed vigorously with sand after which they were washed

with clean water and left to air dry in a closed room to

avoid contamination. In Oslo, the samples were homogenised

together prior to undertaking their respective analytical protocols

in Uppsala, Oslo and Mainz (see below). Samples for pollen

extraction were removed from the right side of the core, packed

into Whirlpaks, and sent to the Ivory Paleoecology Laboratory at

the Pennsylvania State University. Utensils were washed with soap

and water and air dried in a closed room after every sample.

3.2.2 Dating

Determination of ages of sediments and soils from the

study locations was undertaken using both radiocarbon ages of

organic material or charcoal from the core samples and Optically

Stimulated Luminescence (OSL) dating of quartz grains from the

terraces. Samples for accelerator mass spectrometry radiocarbon

dating were carefully selected using clean dental picks and wrapped

in aluminum foil either in the ﬁeld lab or at the Archaeochemistry

Lab of the University of Oslo. Samples from the augers were

submitted to the Radiocarbon Laboratory at Uppsala University

and have been corrected for isotopic fractionation using the 2020

Southern Hemisphere calibration curve (Hogg et al., 2020). Age-

depth models were developed using the “rbacon” package (Blaauw

and Christen, 2011) in the R statistical computing environment

(v.4.20, R Core Team, 2023), with maximum modelled depths

corresponding to the depth of the lowest sample in each sequence

(AU3 =67 cm; AU7 =77 cm; AU8 =146 cm).

We collected OSL samples in light-free, 30-cm carbonized steel

tubes from the cleaned sidewalls of terrace exposures. The tubes

were wrapped in duct tape and transported to the Luminescence

Laboratory of the Korea Basic Science Institute in Ochang,

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Wright et al. 10.3389/fearc.2023.1250871

FIGURE 2

The Mzimba project area showing archaeological sites and sampling locations. Image created in QGIS 3.22 with ASTER Global Digital Elevation Model

(v3) background downloaded from: https://earthexplorer.usgs.gov/. Overlay ESRI panchromatic image obtained from the HCMGIS QGIS plugin.

South Korea, where the sediments were removed and prepared

for analysis under low-wavelength light. Grain sizes of 50–180 µm

were isolated by density separation, etched with hydroﬂuoric acid

and subjected to Single Aliquot Regeneration of small aliquots

(several hundred grains) mounted to 3 mm disks (Bøtter-Jensen

et al., 2000;Murray and Wintle, 2003). The calculation of an

equivalent dose (De) involved ﬁrst measuring discharged radiation

(Gy) in a photomultiplier tube after shooting a beam of blue-

LED light at irradiated aliquots in a Risø reader (Model TL/OSL-

DA-20) ﬁtted with a 90Sr/90Y beta radiation source. Samples

were then bleached, irradiated, heated and stimulated again

with infrared-LED (to remove potential contaminating eﬀects

of feldspar inclusions) after which blue-LED stimulation was

performed for 40s at 150◦C. Dose rates (Dr) were determined

after calculating secular equilibrium of the sediments using low-

level, high-resolution gamma spectroscopy (Liritzis et al., 2013), a

cosmic ray dose contribution (Prescott and Hutton, 1994) and the

degree of radiation attenuation based on the average water content

of the samples over the burial lifetime. For further information,

the methods for sample analysis accord with those studied from

the nearby Karonga region and published in the Supplementary

material of Thompson et al. (2021).

3.2.3 Soil stable isotopes

Soil stable isotopes were used to broadly examine the evidence

for anthropogenic inputs into sediments (δ15N) and relative ratios

of forest and grass cover (δ13C) at the sampled locations. Soil

nitrogen isotope ratios in non-disturbed ecosystems are generally

inversely correlated with rainfall and temperature, and can thus

be used as a general index of aridity (Ambrose, 1991). Plant and

soil δ15N values are also consistently higher in anthropogenic

sediments (Commisso and Nelson, 2006), particularly during the

decomposition of soil organic matter (Natelhoﬀer and Fry, 1988;

Högberg, 1997).

Carbon isotopes in soil are used to identify plant biomass at

sampled locations. Carbon isotopes (δ13C) can be isolated directly

from bulk soil matter, reﬂecting changes in plant spectra based

on photosynthetic pathways (C3, C4, CAM) and CO2production

(Cerling et al., 1989;Ruiz Pessenda et al., 2009). Such datasets

demonstrate relative concentrations of tree (C3) vs. grass (C4)

cover (e.g., Srivastava, 2001;West et al., 2006;Ruiz Pessenda

et al., 2009) and ability of the soils to store CO2(Bowling et al.,

2008;Breecker et al., 2010). In the tropics, C3 plants are generally

comprised of trees and leafy dicots and C4 plants tend to be

grasses (including sorghum, millets, Digitaria sp., African rice and

savannah grasses).

Preparation of samples followed protocols outlined in Wright

et al. (2019) in which sediments for δ13C analysis were pretreated

with 1M HCl for 24 h, dried, and then 25.0 ±0.1 mg were sealed

in tin capsules and loaded into a DeltaV Advantage Stable Isotope

Mass Spectrometer conﬁgured with a Flash Elemental Analyzer

(ThermoFisher) for combustion into puriﬁed CO2and N2at

the CLimate Interpretation of Plant Tissue lab in Department of

Biosciences at the University of Oslo. Laboratory precisions were

measured between 0.03 and 0.04 per mile (‰) for δ13C using

the NBS19 (1.95‰) and LSVEC (−46.6‰) standards as calibrated

against a δ13CVPDB internal standard. Preparation of samples for

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Wright et al. 10.3389/fearc.2023.1250871

δ15N followed the same protocols but were not acidiﬁed prior

to extraction. δ15NAIR internal references and quality assurance

standards were calibrated against USGS40 and USGS41, which have

consensus values of −4.52 and 47.57‰, respectively. Precisions

were determined to be 0.1‰ for the sample runs of δ15N. Statistical

treatment of the data include standard ellipses calculated to the 2-

σ(95%) level and a loess ﬁt using the “lowess” function and were

performed in ggplot2 in RStudio 2022.07.1 (Build 554). All data and

code are available at: https://doi.org/10.6084/m9.ﬁgshare.23092127.

3.2.4 Organic biomarkers

Faecal stanols are organic molecules produced in the guts of

mammals, most especially humans who produce high amounts

of coprostanol; they can be used to detect relative population

sizes on a landscape level (Bethell et al., 1994;Bull et al., 2002;

Evershed, 2008;Zocatelli et al., 2017). High levels of coprostanol

are also found in the faeces of non-human primates and pigs

(family Suidae), but most data show that coprostanol does not

dominate the biomarker spectrum here as much as in human faeces

(Subbiah et al., 1972;Ausman, 1993;Shah, 2007;Sistiaga, 2015;

Prost, 2017;Zocatelli et al., 2017). Faeces of herbivores contain less

coprostanol than humans but higher amounts of 5β-stigmastanol,

providing opportunities to reconstruct the demography of both

humans and ruminant animal communities (Prost, 2017). Bile

acids are an important companion biomarker to stanols because

they allow a diﬀerentiation between primate faeces, the faeces of

pigs and distinct herbivores (Prost, 2017;Zocatelli et al., 2017). n-

Alkanes are found in the epicuticular layer of leaves and can be used

to distinguish litter input from grasses and herbs from broadleaf

trees (Eglinton and Hamilton, 1967;Zech et al., 2010;Bush and

McInerney, 2013).

Faecal biomarkers and n-alkanes were extracted in tandem with

stable isotopes following sample homogenisation. Biomarkers were

extracted by a total lipid extract in a microwave oven after which the

method of Birk (2012) was used for puriﬁcation and derivatisation

with small modiﬁcations. The extract was saponiﬁed and the

biomarkers were recovered from the saponiﬁcation solution by a

sequential lipid-lipid extraction. During this step the bile acids were

separated from the other biomarkers. The bile acids were puriﬁed

by solid phase extraction after methylation. Stanols, 15-sterols and

n-alkanes were separated and puriﬁed by a solid phase extraction,

which yielded n-alkanes and steroids in diﬀerent fractions.

Steroids were measured by gas chromatography mass

spectrometry after silylation (GC/MS; 7000D MS connected to a

7890B GC equipped with a DB-5ms Ultra Inert column, Agilent,

Santa Clara, CA, USA) and n-alkanes by gas chromatography

ﬂame ionization (GC-FID; 7890B GC equipped with a HP5

column, Agilent, Santa Clara, CA, USA). Detailed descriptions of

the analytical procedures and data outputs are provided in the

Supplementary material.

3.2.5 Pollen analysis

Fossil pollen and microscopic charcoal analyses of dambos and

terraces were conducted to reconstruct vegetation and regional-

scale ﬁre in the past. All samples were processed using standard

pollen extraction methods, including digestion of silicates by

hydroﬂuoric acid and removal of organics by acetolysis (Fægri

et al., 1989). Following completion of the 2017 ﬁeld season,

terrace samples were sent to LacCore Facility at the University

of Minnesota for processing. During the extraction phase, a

contaminated batch of microspheres was added to a single batch

of samples (8). For these samples, it was not possible to calculate

charcoal concentrations, and thus microcharcoal is not presented

for these samples only. For the 2019 season, the auger samples were

processed at Penn State University. These were sieved at 10 microns

to remove clays, and Lycopodium spores were added to calculate

concentrations of pollen and charcoal.

Where possible, over 300 pollen grains were counted per

sample; however, preservation of pollen was particularly poor in

samples from AU8 and AU3-3. For these samples, pollen counts

were signiﬁcantly lower, ranging from completely sterile to 57

grains. Samples from these augers are interpreted qualitatively.

The record comprised 49 pollen and plant spore taxa and 5

morphotypes of fungal spores (including Sporormiella). Atlases

of pollen morphology were used for identiﬁcations (Maley, 1970;

Bonneﬁlle and Riollet, 1980) as well as the African Pollen Database

(https://africanpollendatabase.ipsl.fr). For the terrace samples only,

bisaccate grains of Podocarpus and Pinus were not diﬀerentiated,

thus this group is presented as Pinopsida undiﬀerentiated.

This only inﬂuences the youngest terrace samples, as Pinus

was introduced to the region in the twentieth century. Pollen

abundances are calculated based on a sum of all pollen and plant

spores excluding broken grains and aquatics (Cyperaceae, Typha).

Pollen diagrams were produced using the “rioja” package (v.1.0–5,

Juggins, 2022) in R (v.4.20, R Core Team, 2023). Terrestrial pollen

taxa are presented as a percentage of all terrestrial plants; aquatic

pollen taxa are presented as percentage of combined terrestrial and

aquatic plants. Cases where values are consistently lower than 5%

include a 5×exaggeration (lighter shading).

Microcharcoal was diﬀerentiated into two categories based

on aspect ratios (length/width). Following methods presented in

Miao et al. (2019) and Feakins et al. (2020), particles with higher

aspect ratios (length/width >2.5) have been associated with the

burning of grass or sedge, while those with lower aspect ratios

are associated with burned woody material. All data and code are

available at: https://doi.org/10.6084/m9.ﬁgshare.23092127.

4 Results

4.1 Sedimentation

Radiocarbon (Table 1) and OSL (Table 2) ages from the dambo

and terrace sequences, respectively, situate the environmental and

archaeological sequences of the present study to beginning in the

Late Pleistocene and continuing through into the late twenteeth

century CE. Sediment cores extracted from wetland environments

and pits excavated into terraces of the Kasitu River exposed in

secondary drainageways demonstrate relatively slow sedimentation

from the Pleistocene to the Middle Holocene (Figures 3,4). Three

proﬁles with coverage from this time period with absolute ages

show accumulation rates from 19.0 to 8.6 ka (AU8) of 0.07

mm/yr, 0.09 mm/yr (Kasitu 4, 135cm between 34.6 and 18.8

ka), and 0.25 mm/yr (Kasitu 2, 90 cm between 7.1 and 3.5 ka).

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TABLE 1 Radiocarbon ages from environmental sampling of the Mzimba District, Malawi.

Lab # MALAPP

code

Corresponding

proxy (Figure 3)

Material δ13C14 C age 2-σcal yr BP

Ua-69522 ISO29 POL31 Fine sandy loam −16.2 15742 ±59 18850–19111

Ua-69523 ISO31 POL33 Clay None 7759 ±124 8223–8984

Ua-69524 ISO33 POL35 Coarse sandy loam −23.7 1794 ±32 766–921

Ua-69525 ISO42 POL36 Clay loam −16.2 101.8 ±0.3∗AD 1958–2000

Ua-69526 ISO45 POL39 Fine sandy clay loam −16.9 792 ±27 657–728

Ua-69527 ISO47 POL41 Silt loam −17.1 1233 ±28 989–1179

Ua-69528 ISO48 POL42 Silt loam −18.1 927 ±28 727–904

Ua-69529 ISO50 POL44 Fine sandy loam −10.5 2388 ±37 2153–2680

Ua-69824 ISO8 POL8 Silt loam −15.3 964 ±29 766–921

Ua-69825 ISO9 POL9 Clay loam −14.8 267 ±29 146–433

Ua-69826 ISO10 POL10 Clay loam −14.6 49 ±29 Suess eﬀect

Ua-69827 ISO11 POL11 Clay loam −16.8 104.0 ±0.4∗AD 1958–1999

Ua-69828 ISO30 POL32 Clay −16.2 9690 ±51 10744–11200

Ua-69829 ISO43 POL37 Clay loam −15.9 149 ±29 Suess eﬀect

∗pMC

Radiocarbon ages calendar corrected for atmospheric production of radiocarbon (Hogg et al., 2020) in OxCal 4.4. Samples Ua-69525 and Ua-69827 were calibrated using the Calib post-bomb

correction curve (http://calib.org/CALIBomb/) and reported in years AD.

However, accumulation rates for sections with absolute ages after

the Middle Holocene are much greater. The Luwelezi proﬁle

(247 cm of deposition between 1.2 and 0.2 ka =2.47 mm/yr)

has multiple inferred periods of landscape stabilisation based on

palaeosol formation, and Kasitu 5 (130 cm of deposition but two

indistinguishable ages within the 1-σstatistical error of 0.4 ±0.02

ka, has two inferred periods of landscape stabilisation. Sediment

cores with radiocarbon ages (AU3, AU7) also show accumulation

rates >1 mm/yr after 1 ka. The historical deposition and erosion

rate is also supported through conversations with local farmers

and lifelong residents; for example, one informant described a time

about ca. 2010–2015 when he could see large cobbles at the base

of the Luwelezi stream. Today, this tributary to the Kasitu is a ﬂat-

bottomed and silty perennial waterway. Examples of recent erosion

are clearly observable in road and water cuts, including some with

pottery sherds buried under more than 1 m of sediment.

4.2 Stable isotopes

Light stable isotopes (δ13C, δ15 N) extracted from sediments

and soils show an inverse correlation between 13C and

15N (Supplementary Table 1;Figure 5). Uneven coverage of

radiometric ages and variable preservation of nitrogen in the

sediments obfuscates time-transgressive correlations of carbon

and nitrogen isotopes. However, plotting of 13C values using

stratigraphic inference with ages shows increasingly heavier

isotopic composition over time with a relatively unchanging

value of ∼-22‰ spanning from ca. 8–2.5 ka and rapid isotopic

enrichment thereafter relative to the preceding ca. 20 kyr

(Figure 6).

4.3 Biomarkers

AU7 was analysed quantitatively for n-alkanes, faecal bile acids

and faecal stanols as well as related steroids (Tables 3,4;Figure 7).

Long-chain n-alkanes (C26–C33) had concentrations of ≤40

µg/gTOC (Table 3), the faecal 5β-stanols had concentrations ≤4

µg/gTOC, the precursor substances of these biomarkers, 15-sterols,

had concentrations ≤141 µg/gTOC and 5α-stanols, the reduction

products of 15-sterols, which are formed in the environment

outside of the gut of mammals, had concentrations ≤38 µg/gTOC

(Table 4 and Supplementary Table 4). Bile acids had concentrations

≤14 µg/gTOC (Supplementary Table 5).

The ratio of the concentrations of long-chain n-alkanes with

odd numbers of carbon vs. long-chain n-alkanes with even numbers

of carbon [odd-over-even predominance; OEP; (C27 +C29 +

C31 +C33]/[C26 +C28 +C30 +C32)] can be used to identify

higher plant biomass inputs into sediments as well as determining

the degree of degradation of n-alkanes (Eglinton and Hamilton,

1967;Hoefs et al., 2002;Zech and Glaser, 2008;Buggle et al.,

2010;Bush and McInerney, 2013). Ratios ≥4 are characteristic

for n-alkane inputs from higher biomass plants (Hoefs et al.,

2002;Zech and Glaser, 2008). Only the lowermost sample and the

uppermost sample from AU7 (ISO50 at −80.5cm dating to ca. 2.3

ka and ISO42 at −2.5 cm dating to AD1958-2000) had an OEP

value <4 (Table 3) indicating dominance of aquatic or degraded n-

alkanes. These samples were therefore excluded from the following

consideration of the terrestrial inputs of plant biomass. All other

samples had OEP values ≥6 (Table 3). Chain lengths C27 and

C29 are the dominant chain lengths in broadleaf trees, and chain

lengths C31 and C33 have a high abundance in grasses and other

herbaceous plants (Buggle et al., 2010;Zech et al., 2010;Bush

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TABLE 2 Optically Stimulated Luminescence ages from environmental context sampling of the Mzimba District, Malawi (Figure 4).

Sample;

Sample loc.

Depth

(cm) §

Water

content∗

(wt. %)

238U

(Bq·kg−1)

226Ra

(Bq·kg−1)

232Th

(Bq·kg−1)

40K

(Bq·kg−1)

Dry

betaa

(Gy·ka−1)

Dry

gammaa

(Gy·ka−1)

Cosmic

rayb

(Gy·ka−1)

Total dose

rate

(Gy·ka−1)

De(Gy) nAgec

(ka)

MAL17–1; Kasitu

75 4 ±1 32.9 ±8.3 26.3 ±0.6 91.5 ±3.1 831 ±14 2.91 ±0.11 1.97 ±0.04 0.22 ±0.02 4.88 ±0.12 11.4 ±0.5 16 2.3 ±0.1

MAL17-2; Kasitu

25 3 ±1 15.9 ±8.2 24.5 ±0.6 91.9 ±3.1 962 ±16 3.17 ±0.12 2.06 ±0.04 0.25 ±0.02 5.30 ±0.12 7.2 ±0.4 16 1.4 ±0.1

MAL17-3; Kasitu 2 155 3 ±1 26.6 ±7.2 30.4 ±0.6 116.9 ±3.6 1068 ±16 3.65 ±0.13 2.50 ±0.04 0.19 ±0.02 6.14 ±0.14 43.5 ±2.0 16 7.1 ±0.4

MAL17-4; Kasitu 2 65 3 ±1 32.0 ±9.5 32.8 ±0.7 141.7 ±4.4 1168 ±19 4.08 ±0.15 2.90 ±0.05 0.23 ±0.02 6.94 ±0.16 24.2 ±1.3 14 3.5 ±0.2

MAL17-6; Kasitu 4 235 2 ±1 43.3 ±7.7 27.9 ±0.6 77.6 ±2.7 479 ±10 2.02 ±0.08 1.54 ±0.03 0.17 ±0.02 3.63 ±0.09 125.7 ±5.9 15 34.6 ±1.8

MAL17–7; Kasitu 4 100 8 ±2 53.1 ±6.0 41.7 ±0.6 114.1 ±3.5 545 ±10 2.51 ±0.09 2.14 ±0.05 0.21 ±0.02 4.45 ±0.11 83.8 ±2.6 11 18.8 ±0.8

MAL17-8; Luwelezi 315 14 ±3 23.5 ±7.8 11.6 ±0.6 78.1 ±2.8 621 ±12 2.20 ±0.09 1.54 ±0.03 0.15 ±0.01 3.34 ±0.11 4.0 ±0.1 15 1.2 ±0.1

MAL17–9; Luwelezi 130 5 ±1 5.9 ±60.6 7.6 ±0.6 43.6 ±2. 767 ±14 2.24 ±0.09 1.20 ±0.02 0.20 ±0.02 3.46 ±0.09 2.3 ±0.3 14 0.7 ±0.1

MAL17–10;

Luwelezi

68 3 ±1 2.4 ±2.4 4.0 ±0.5 20.2 ±1.5 715 ±16 1.91 ±0.07 0.84 ±0.02 0.23 ±0.02 2.89 ±0.08 0.6 ±0.1 12 0.2 ±0.0(1)

MAL17-11; Kasitu 5 190 4 ±1 1.4 ±5.3 14.1 ±0.6 41.6 ±2.1 1054 ±22 2.92 ±0.11 1.44 ±0.03 0.18 ±0.02 4.35 ±0.12 1.6 ±0.1 15 0.4 ±0.0(2)

MAL17-12; Kasitu 5 60 3 ±1 40.2 ±6.5 31.9 ±0.7 122.8 ±4.6 560 ±15 2.49 ±0.10 2.19 ±0.05 0.23 ±0.02 4.76 ±0.11 1.9 ±0.1 12 0.4 ±0.0(2)

§Depths of the samples are the vertical distance from the modern ground surface. ∗Present water contents (±20 % of uncertainty). aData from high-resolution low level gamma spectrometer were converted to inﬁnite matrix dose rates using conversion factors given

in Liritzis et al. (2013). bCosmic ray dose rates were calculated using the equations given by Prescott and Hutton (1994). cCentral age ±1σstandard error. The targeted mineral was quartz with diameters of 90-250µm. Measurement mode: SAR protocol, preheat at

240 oC (samples KT2992, 2995, 2996. 2997, 2998, 2999) or 260oC (samples KT2988, 2989, 2990, 2991, 2993, 2994) for 10 s, multiple grain single aliquots (three 8mm aliquots for each sample).

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FIGURE 3

Schematic proﬁles of wetland auger tests from the Mzimba region, Malawi showing sedimentation, soil development, and the locations where

samples were taken from the cores. AU3 and AU7 were extracted in sequences using a percussion auger to access deeper aspects of the landform

until refusal occurred. Sediment and soil classiﬁcation schemes follow the USDA standards as outlined in Schoeneberger et al. (2012).

and McInerney, 2013). The ratios of the n-alkanes C27 and C29

to the n-alkane C33 are therefore high with an input of litter

originating from deciduous trees and low with an input of biomass

originating from grasses. n-Alkane ratios (C27/C33 =0.2 and

C29/C33 =0.9, Figure 6) indicate a strong decrease in forest

cover from ISO47 at −53 cm (ca. 1 ka) relative to the underlying

(earlier) samples (C27/C33 ≥0.3 and C29/C33 ≥1.1; Figure 7;

Supplementary Table 3).

ISO47 further shows high concentrations of the faecal

biomarkers coprostanol (5β-cholestan-3β-ol; 1.4 µg/gTOC) and

epi-coprostanol (5β-cholestan-3α-ol; 1.3 µg/gTOC), indicative of

the presence of omnivores such as humans, non-human primates or

pigs (Table 4). However, other stanols had also high concentrations

at this depth (Table 4) and background values of faecal biomarkers

were found in soils and sediments where no enhanced deposition

of faeces was assumed (Bethell et al., 1994;Evershed et al., 1997;

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FIGURE 4

Schematic proﬁles of alluvial terraces from the Mzimba region, Malawi showing sedimentation, soil development and the locations where samples

were taken from the proﬁles. Sediment and soil classiﬁcation schemes follow the USDA standards as outlined in Schoeneberger et al. (2012).

Bull et al., 2001). To correct for these background values, the

amounts of coprostanol and its epimer were related to the amounts

of cholestanol (5α-cholestan-3β-ol), which is the reduction product

of cholesterol (15-sterol) that is mainly formed outside of the

gut of mammals ([coprostanol +epi-coprostanol]/cholestanol,

Bull et al., 2002). This ratio showed high values in ISO47 (0.3)

in relation to the other samples indicative for faeces inputs

(Figure 7). Although coprostanol and its epimer can also be

found in the faeces of herbivores, the more speciﬁc biomarkers

for faeces of herbivores are 5β-stigmastanol (5β-stigmastan-3β-

ol) and epi-5β-stigmastanol (5β-stigmastan-3α-ol), which are the

reduction products of phytosterols, due to the high concentrations

of the phytosterols in their diet (Leeming et al., 1996;Tyagi

et al., 2008;Gill et al., 2010;Prost, 2017). The ratio (coprostanol

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FIGURE 5

Biplot of δ13C (vs. PDB) and δ15 N (vs. AIR) values of soils from the Mzimba region, Malawi. The red dashed line shows an r2value of −0.413 showing

inversely correlated enrichment of isotopic values (P=0.0187, df =30).

FIGURE 6

Time-transgressive loess plot of δ13C (vs. PDB) of soils from the Mzimba region, Malawi with ordination of approximate ages made by stratigraphic

inference relative to absolute ages. The red dotted line shows an r2value of +0.59.

+epi-coprostanol)/(5β-stigmastanol +epi-5β-stigmastanol) was

calculated to diﬀerentiate between faeces of omnivores and

herbivores (high values indicate higher inputs of omnivorous

faeces and lower by inputs of herbivorous faeces). This ratio

also had a high value in ISO47 (0.5, Table 4). The bile acid

patterns of AU7 showed a dominance of deoxycholic acid, the

presence of lithocholic acid and the absence of hyodeoxycholic

acid (Supplementary Table 5). Therefore, the omnivorous faeces

were likely derived from primate sources rather than pigs (Tyagi

et al., 2008;Prost, 2017). The more pronounced domination of

coprostanol in the biomarker patterns of human faeces in relation

to non-human primate faeces (Subbiah et al., 1972;Ausman, 1993;

Shah, 2007;Sistiaga, 2015;Prost, 2017;Zocatelli et al., 2017), and

the close proximity of the test site to the Hora 1 archaeological site,

which is densely packed with anthropogenic refuse, suggests that

the faeces derived from omnivores was most likely from humans.

Between −44 cm (ISO46) and −34 cm (ISO45 dating to

0.7 ka), there is an increase in forest cover indicated by

an increase in C27/C33 ratios to 0.4 and C29/C33 to 1.0

(Figure 7). However, alkane ratios in ISO45 were still lower

than in the period before the forest decrease shown in the

lower samples (ISO49). This period of aﬀorestation is succeeded

by an indication of a decrease in forest cover at −26 cm

(ISO44) based on C27/C33 ratios of 0.2 and C29/C33 to 0.4,

coupled with high values of the ratios that are indicative for

omnivorous faeces [(coprostanol +epi-coprostanol)/cholestanol of

0.2 and (coprostanol +epi-coprostanol)/(5β-stigmastanol +epi-

5β-stigmastanol) of 0.3; Figure 7 and Table 4]. The sample above

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TABLE 3 Quantities of long chain n-alkanes (µg/gTOC ) and odd-over-even predominance [OEP (C27 +C29 +C31 +C33)/(C26 +C28 +C30 +C32)]

from AU7, Mzimba region, Malawi.

Sample

number

Mean

depths

C26 C27 C28 C29 C30 C31 C32 C33 OEP

(cm) (µg/gTOC) (µg/gTOC ) (µg/gTOC) (µg/gTOC ) (µg/gTOC) (µg/gTOC ) (µg/gTOC) (µg/gTOC)

ISO42 2.5 31 26 25 23 14 30 11 37 1

ISO43 15 2 7 2 16 2 20 2 38 9

ISO44 26.25 4 6 3 14 2 15 2 33 6

ISO45 33.75 3 10 3 23 2 19 3 24 7

ISO46 44 4 8 5 31 4 24 2 36 7

ISO47 53 4 8 4 34 3 22 5 39 7

ISO48 58 2 9 3 36 4 26 3 32 9

ISO48 58 2 9 5 37 2 30 <LOQ 29 11

ISO49 69.75 0 7 4 16 4 16 <LOQ 10 6

ISO50 80.5 6 5 5 14 0 13 <LOQ <LOQ 3

LOQ, limit of quantiﬁcation.

(ISO43) dates to within the last 300 years and shows stability in

grass vs. trees present on the landscape. The penultimate sample

(ISO42) showed high quantities of several steroids but the stanol

ratios did not show especially enhanced input of omnivorous

faeces [(coprostanol +epi-coprostanol)/cholestanol of 0.1 and

(coprostanol +epi-coprostanol)/(5β-stigmastanol +epi-5β-

stigmastanol) of 0.2; Figure 7,Table 4, and Supplementary Table 4].

A full data presentation of the results of biomarker analyses are

found in the Supplementary material.

4.4 Pollen reconstruction

Fossil pollen concentrations were generally high in the auger

samples (6,327 grains/cm3), apart from augers AU3-3 and AU8

(average =447 grains/cm3). AU3-3 was sterile except for a few

poorly preserved pollen grains and will not be discussed in the

results. Within samples where 300 grains counts were achieved,

broken, and/or crumbled grains were generally low (<3.5%;

Figure 8).

AU8 was a core from ∼1360 m AMSL in an open swale

surrounded by woodland about 8 km west of the Kasitu River and

3.75 km west of the HOR-1 site. It is not presently under cultivation.

The oldest samples in this unit are late Pleistocene (ca. 19 ka) and

extend to the late Holocene (1.6 ka). Pollen concentrations were

low in these samples (average =656 grains/cm3); however, pollen

was observed in all samples and as these include some of the oldest

dated samples in our record, we report here the qualitative presence

of key pollen taxa. Overall, these samples were dominated by

Poaceae pollen, while other herbs like Asteraceae were consistently

present. Cyperaceae pollen was generally near the lowest values of

all pollen samples in this interval (mean =22.5%) and tree pollen

presence was sporadic.

AU7 was a core from ∼1425 m ASML in a sparsely wooded

grassy swale about 3.75 km west of the Kasitu River and 0.6 km

southeast of the HOR-1 site. This site is not presently under

agriculture. These samples cover ca. 2.6 kyr of the late Holocene

and were recovered from a dambo wetland that is subject to

slow, seasonal sedimentation. These samples were dominated

throughout by aquatic pollen taxa such as Cyperaceae (mean=

212% relative to the terrestrial pollen sum), in particular Ascolepis

(mean =36%; Cyperaceae family). Of the terrestrial pollen taxa,

Poaceae reached maximum values in a sample dated to 0.8 ka,

then decreased minimally until present. Tree pollen was present

in the pre-modern samples in lower abundances (8%) until an

increase in Podocarpus and Pinus in the most recent two samples

(24%, 5%). Microcharcoal increased from the pre-modern (mean

=11,617 particles/cm3) to the modern samples (mean =106,499

particles/cm3), with charcoal with high aspect ratios indicating a

grassy source dominating.

AU3 was a core from ∼1320 m ASML in a seasonally ﬂooded

grassland about 12 km west of the Kasitu River and 11.5 km

northwest of the HOR-1 site. It is not presently under agriculture

and is surrounded by dense woodland. These samples cover ca. 1

kyr of the Late Holocene and were dominated by aquatic pollen

taxa like Cyperaceae (mean =133% relative to the terrestrial

pollen sum), especially Ascolepis (17%). Of the terrestrial pollen,

Poaceae was generally high but decreased values in the most

recent sample (range =27–46%). Additionally, other herbaceous

pollen taxa were present, including Asteraceae, which also

increased in the most recent sample (range =0–3%). Tree pollen

taxa followed a similar patter to AU7 with lower abundances

characterized in the pre-modern samples by Brachystegia (mean

=6%) until the most recent sample, where Podocarpus and Pinus

dominated (52%, 10%). Microcharcoal increased over an order of

magnitude from the pre-modern (mean =4,947 particles/cm3)

to the modern samples (mean =38,917 particles/cm3),

with charcoal with high aspect ratios indicating a grassy

source dominating.

The terrace samples presented in Figure 8D are a synthesis of

pollen samples taken from proﬁles Kasitu 2, Kasitu 5, and Luwelezi

terraces and range in age from 8ka to modern. The general patterns

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Wright et al. 10.3389/fearc.2023.1250871

TABLE 4 Quantities of stanols (ng/gµg/gTOC) and the ratio (coprostanol +epi-coprostanol)/(5β-stigmastan-3β-ol +5β-stigmastan-3βα-ol) from AU7, Mzimba region, Malawi.

Sample

number

Mean

depths

Coprostanol

(5β-

cholestan-

3β-ol)

epi-Coprostanol

(5β-cholestan-

3α-ol)

5β-Stigmastanol

(5β-stigmastan-

3β-ol)

epi-5β-

Stigmastanol

(5β-stigmastan-

3α-ol)

Cholestanol (5α-

cholestan-3β-ol)

Stigmastanol

(5α-stigmastan-

3β-ol)

(Coprostanol+epi-

coprostanol)/(5β-

stigmastanol+epi-

5β-stigmastanol)

(cm) (µg/gTOC) (µg/gTOC ) (µg/gTOC) (µg/gTOC ) (µg/gTOC) (µg/gTOC )

ISO42 2.5 0.7 0.5 3.9 1.2 8.3 37 0.2

ISO43 15 0.1 0.1 1.6 0.7 6.2 17 0.1

ISO44 26.25 0.1 0.4 1.1 0.5 3.4 17 0.3

ISO45 33.75 0.2 0.2 1.4 0.7 4.5 13 0.2

ISO46 44 0.2 0.3 1.8 1.1 9.7 17 0.2

ISO47 53 1.4 1.3 3.7 1.9 8.0 19 0.5

ISO48 58 0.3 0.4 1.9 1.1 9.4 18 0.2

ISO48 58 0.3 0.4 1.9 1.1 9.5 18 0.2

ISO49 69.75 0.3 0.5 1.6 1.3 12.5 19 0.3

ISO50 80.5 0.5 0.6 1.5 1.7 9.4 18 0.3

in the pollen assemblages shows a dominance of trees, particularly

Pinopsida undiﬀerentiated (20–40%) until the last 2 kyr. Given

that Podocarpus pollen is the only native genus in this class, it is

likely this phase was dominated by Podocarpus. At 2 ka, there was

a notable increase in herbaceous pollen taxa, especially Poaceae

(60%). Finally, in the samples from the last 100 years, there is an

increase in pollen of Pinosopida undiﬀerentiated (55–60%) and

other trees. As the Pinus was introduced within this window and

auger samples observe an increase in this genus, it is likely that

this last increase represents an increase in both gymnosperms in

the last century.

5 Discussion

Our integrated archaeo-ecological investigation of the Mzimba

region of northern Malawi indicates that there are critical ecological

inﬂection points associated with diﬀerent human settlement and

subsistence regimes in the past. The stable isotopic composition of

the sites demonstrates a clear inverse correlation between 15N and

13C values. From soils and sediments, more positive 15 N values and

more negative 13C values are indicative of higher concentrations

of leaf litter and/or canopy, which biases the evapotranspiration

of lighter isotopes (14N, 12 C) in the forms of NO2and CO2

(Natelhoﬀer and Fry, 1988). Overall, the time-transgressive trend

observed from the carbon isotopes studied (δ13C) demonstrate

a stronger tendency toward grassier landscape conditions from

the start of the Holocene (Figure 6) with the caveat that the

sample size is small before the Middle Holocene. However, these

data are supported by the n-alkane data from AU7 (Figure 7)

and pollen (Figure 8), which also show grass/herbaceous-dominant

conditions, particularly within the last ∼2 kyr.

Grass-dominant ecological niches that favour domesticated

animals have been reconstructed across Africa correlating to the

times when animal production is ﬁrst documented in speciﬁc

regions (Phelps et al., 2020). Farming and animal production

are known to leave long legacies within soils on landscapes that

can be measured from nutrient pools for millennia following

site abandonment (Marshall, 2018;Cao et al., 2021;Storozum

et al., 2021). The data from the Mzimba District have similarly

left geochemical traces, supported by pollen data, indicating

that human activities related to the introduction of agriculture

also impacted land cover conditions, despite a lack of direct

macro-archaeological evidence for the introduction of farming

technologies at the sites we were testing. The oldest date for Iron

Age agro-pastoralists in the Kasitu region is ca. 1.6 ka, which

is taken from Munga Hill (Sinclair, 1991), ∼1 km north of the

Luwelezi proﬁle (Robinson, 1982) and is similar to the oldest dates

for food producers in Malawi from the southern part of the country

(Juwayeyi, 2011).

Microarchaeological data indicates changing land cover

conditions in relation to diﬀerent land use strategies in the later

Iron Age. Faecal biomarkers in the auger test adjacent to the HOR-

1 site show increased input from omnivores during the period we

interpret as representing initial food production at our test location,

dating to around 1 ka. This was sustained until ca. 0.6 ka, when

the n-alkane and pollen results show recovery of forest conditions

and low presence of omnivores (in this case, humans). Omnivore

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Wright et al. 10.3389/fearc.2023.1250871

FIGURE 7

Ratios of the n-alkanes C27/C33 and C29/C33 on the left, with high values showing a higher input of biomass of broadleaf trees and low values a

higher input of grasses and other herbaceous plants. Ratio of (coprostanol +epi-coprostanol)/cholestanol with high values characteristic for inputs

of omnivorous faeces (likely from humans) from AU7, Mzimba region, Malawi.

populations then apparently rebounded and then increased further

within the historical period. These patterns may indicate episodic

settlement and land-use strategies in the second half of the Iron

Age, or they may reﬂect a larger pattern of population decrease.

Charcoal data from this sample in the core shows a slight increase

in particle concentrations and some of the highest proportions of

sedges, suggesting that waterlogged soils may have discouraged

local cultivation and human occupation, while these activities

continued outside the drainage catchment of the swale from which

the core was collected.

The pollen and microcharcoal data are in general agreement

with the other proxies studied, but they also indicate additional

landscape formation processes that are important to the human

ecology of the region. First, Cyperaceae pollen, reﬂecting wetland

sedges, persisted throughout all periods of study and are evidence

of continuation of seasonal wetland conditions in the studied

locations from the Late Pleistocene to present (or nearly present)

day. Second, increases in Podocarpus and Pinus (tree) taxa in the

last 200 years occurred in the auger samples despite evidence for

increased concentrations of microcharcoal, which is in general

contrast to expected results based on simulated (Keane et al.,

2004;D’Odorico et al., 2006;Phelps et al., 2020) and observed

(Bakker et al., 2013;Marchant et al., 2018;Leunda et al.,

2020) occurrences in ecological research. However, spatially and

taxonomically complex ecological simulations challenge simplistic

ﬁre-driven forest-to-savannah formation models, demonstrating

that ﬁres consume saplings and seedlings that contribute negligibly

to biomass (Hanan, 2008). Therefore, the presence of increased

woody vegetation in combination with increased ﬁre occurrence

in the later phases of landscape formation in the Kasitu Valley

are interpreted as reﬂecting spatially heterogenous landscape

management processes in which some patches of mature forest

persisted at various points even as portions of the uplands adjacent

to Luwelezi and Kasitu 5 rapidly eroded, presumably as an eﬀect

of forest cover loss. Of the 111 known species of Pinus, none are

endemic to Africa south of the equator and only one species is

recorded in tropical Asia (Price et al., 1998). Therefore, the presence

of pines in Malawi, recorded in the pollen abundances from the

auger samples, is commonly understood to be an introduction

associated with disturbance ecologies within the last 200–300 years

(Richardson, 1998). It is also important to consider that pollen

and microcharcoal are more often wind-borne then other proxies

such as n-alkanes, faecal biomarkers and bulk stable isotopes, which

likely reﬂect more localised vegetation conditions. Introduced

Pinus stands are currently maintained on the Viphya Plateau

immediately to the east of the Kasitu Valley.

Based on the total available evidence, the most signiﬁcant

ecological inﬂection point occurs in the Late Holocene at the time

in which Iron Age agro-pastoralists are archaeologically identiﬁed

in the region (Juwayeyi, 1981,1991,2008,2011;Robinson,

1982;Davison, 1991). Although preservation of organic matter

was variable and aﬀects the robustness of the interpretations,

the general indicators of plant and faunal ecologies corroborate

sedimentation values, suggesting that after the introduction of

farming techniques to this region of southern-central Africa, the

landscape became generally more open and discharge from the

uplands, where sediments are more prone to erosion, accelerated.

More recent settlement (dating to within the last 75 years)

shows accelerated modes of spatial heterogeneity with increasing

abundances of Podocarpus pollen, while n-alkane and carbon

isotope values show grassier ecological conditions predominate

relative to samples analysed from the Middle Holocene and earlier.

Archaeological and ethnographic proxy data suggest that

impacts in more recent times have inﬂuenced landscape formation

in an accelerating manner. The presence of iron-working sites

outside the rockshelters are not well dated and did not occur

within the lifetimes of most residents of the Mzimba region,

but residents over the age of 60 remember their elders talking

about iron smelting. The bloomeries also appear to not have

been abandoned for long periods of time, with some furnaces

transitioning from nearly complete and standing in 2016 (at the

onset of MALAPP) to a current state of collapse, corroborating

ethnographic accounts. A radiocarbon age analysed from the

inside of a tuyere at the HOR-1 site was determined to be 40

±25 yr BP (cal AD 1816–1956; UGAMS-30619) indicating that

smelting was ongoing into recent times. However, today the most

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Wright et al. 10.3389/fearc.2023.1250871

FIGURE 8

Fossil pollen from three sediment cores in the Mzimba region, Malawi. Darker shades inset within taxonomic categories indicate 5×percent value

relative to the lighter shade. Sites included are (A) AU3, (B) AU7, (C) AU8 and (D) aggregated data from Kasitu 2, Kasitu 5, and Luwelezi terraces.

Frontiers in Environmental Archaeology 16 frontiersin.org

Wright et al. 10.3389/fearc.2023.1250871

obvious local footprints of human environmental inﬂuence are

ﬁrewood collecting and charcoal production which are supported

by the 13C data, but the faecal biomarker data suggests that

the number of people living (and/or defaecating) in the area is

within or less than the general historical level. Thus, we interpret

the current mosaic grassland/forest interspersed with seasonally

ﬂooded dambos in the Mt. Hora region to be a long-term legacy

landscape with multiple stages of transition overprinted on prior

anthropic states rather than an unprecedented historical ecological

condition. Simultaneously, sedimentation rates even within the

last ca. 0.4 kyr from the Kasitu terraces demonstrate that there

has been another inﬂection point in erosion, sedimentation, and

vegetation change over the historical period and accelerating into

the present day.

6 Conclusion

Multiproxy biogenic data from the Mzimba region indicate that

the region consisted of mixed woodland/grassland taxa during the

terminal Pleistocene with an increase in woodland in the Early

Holocene. Land cover transitioned to more open conditions by

the Middle Holocene, which accords with increased evidence for

ﬁre, particularly after 3 ka, which is when the genetic replacement

of hunter-gatherer-foragers with Bantu-speaking people ancestrally

connected to modern populations occurs in the archaeological

record (Skoglund et al., 2017;Lipson et al., 2022) and technologies

associated with farming in this region are ﬁrst documented

(Robinson, 1982). Geomorphic and sedimentologic data from

alluvial terraces support microarchaeological results indicating that

ﬁres and land clearance accelerated by ca. 1.2 ka and induced

signiﬁcant amounts of erosion of the uplands. Biomarkers prior to

and during this period indicate an increase in human settlement

next to the HOR-1 rockshelter and all proxies studied point to a

transition to a more open, grassier landscape in the Late Holocene.

Finally, aﬀorestation associated with commercial timber farming

of introduced pine species over the last several decades attest to

ongoing anthropogenic impacts.

There is an apparent link between the novel introduction

of farming and associated technologies and ecological changes

exceeding the pace of natural climate variability alone. Our

long human-ecological record supports the hypothesis that

the formation of anthropogenic landscapes is temporally and

conceptually divorced from the Industrial Revolution or other

supposed stratigraphic markers of the Anthropocene, calling into

question the epistemological value of this epoch outside the ﬁeld

of geochronology (Ruddiman et al.,2015;2020;2018). The data

we present here demonstrate a notable processual connection

between agro-pastoralism, erosion and vegetation change, which

has left a clear footprint on the modern landscape. Although

lacking in the global synchronicity of expression that comes from

an extra-terrestrial meteor impact, the spread and intensiﬁcation

of farming technologies globally after 3 ka (Stephens, 2019;

Morrison, 2021) is akin to other stratigraphic boundary events.

For example, the Late Ordovician to Silurian transition or Early

to Middle Pleistocene in the palaeontologic records are far more

coarsely resolved, but also lack precise synchronicity and unfold

correlatively and diachronically - just as global human impacts

on landscape formation due to intensive hunting and gathering,

land domestication and globalisation processes can be ascertained

today (Edgeworth et al., 2015;Williams et al., 2022). The results

presented in this study underscore the complexity, heterogeneity,

and overprinting of human impacts across landscapes with deep

settlement histories.

Data availability statement

The data and code presented in the article have been uploaded

to the Figshare repository and can be accessed using the following

doi: 10.6084/m9.ﬁgshare.23092127.

Author contributions

DW, JT, SI, and JB contributed to conception and design of

the study. JT, JD, DW, and PK conducted ﬁeldwork and collected

samples. Samples were analysed by DW, SI, JB, and J-HC. DW

and BD organized the database and performed the statistical

analyses. DW and JT wrote the ﬁrst draft of the manuscript.

DW, JT, SI, JB, and J-HC wrote sections of the manuscript. All

authors contributed to manuscript revision, read, and approved the

submitted version.

Acknowledgments

The Malawi Department of Museums and Monuments

provided permission for the research. Land access was facilitated

by Paramount Chief Inkosi ya Makosi M’Mbelwa V, Inkosi

Chindi, Inkosi Kampingo Sibande, Inkosana Thomas Nkosi,

Mzimba Heritage Association, and the generosity of the Mzimba

community. Sample recovery and preparation in the ﬁeld was

facilitated by participation from oﬃcials from the Malawi

government, the Mzimba community, and students from Malawian

and international universities. JT received funding for ﬁeldwork

and sample analysis from the Wenner-Gren Foundation (Grant

no. 9437), the National Geographic Society, Yale University, and

Hyde Family Foundations. DW received funding from a start-up

grant from the University of Oslo for stable isotope and biomarker

extractions and/or analytical costs. SI received funding from the

National Science Foundation Division of Environmental Biology

Grant #2049982. Stefanie Klassen provided technical assistance

with the biomarker analyses at the University of Mainz. Vendela

Bergin Hansen prepared the stable isotope samples for study and

William Hagopian at the UiO CLIPT lab analysed the samples

using EA-IRMS. The authors would like to thank editor Sjoerd

Kluiving and reviewers David Kaniewski and Harald Stollhofen for

their comments and critiques, which improved the quality of the

ﬁnal manuscript.

Conﬂict of interest

The authors declare that the research was conducted in the

absence of any commercial or ﬁnancial relationships that could be

construed as a potential conﬂict of interest.

Frontiers in Environmental Archaeology 17 frontiersin.org

Wright et al. 10.3389/fearc.2023.1250871

The author DW declared that they were an editorial board

member of Frontiers, at the time of submission. This had no impact

on the peer review process and the ﬁnal decision.

Publisher’s note

All claims expressed in this article are solely those of the

authors and do not necessarily represent those of their aﬃliated

organizations, or those of the publisher, the editors and the

reviewers. Any product that may be evaluated in this article, or

claim that may be made by its manufacturer, is not guaranteed or

endorsed by the publisher.

Supplementary material

The Supplementary Material for this article can be found

online at: https://www.frontiersin.org/articles/10.3389/fearc.2023.

1250871/full#supplementary-material

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Frontiers in Environmental Archaeology 20 frontiersin.org

Occurrence and distribution of biomarkers in loess-paleosol sequences of Tajikistan (Central Asia): Implication for archaeo-ecological studies

Article

Dec 2024
JASR

Finding biomarkers preserved in loess-paleosol sequences is challenging and rarely undertaken in the archaeological studies that occur in these settings. Here, we investigate the preservation of n-alkanes and PAHs collected in association with “Loessic Paleolithic” sites (archaeological sites entrained in fine-grained eolian sediments dating to the Paleolithic era 700,000 to 70,000 years ago) in the Khovaling region of southern Tajikistan. This region has been subject to archaeological inquiry since Soviet research projects in the 1970s found evidence of hominin occupations from Lower and Middle Paleolithic stone tool assemblages in excavations. Questions about the timing and ecological circumstances of putative ancient migrations into the region have prompted new geoarchaeological research at the sites of Lakhuti-IV, Obi-Mazar, Kuldara, and Khonako-II to constrain landscape evolutionary histories better using vegetation (straight-chain [n-]alkanes) and fire (polycyclic aromatic hydrocarbon [PAH]) biomarkers. We collected sediment samples from on–, sparse on–, near-, and off-site contexts relative to known archaeological sites for biomarker extraction and identification. The homologous series of n-alkanes ranging from nC15-nC33 are identified and quantified, in which the long-chain length of n-alkanes (nC27-nC33) has shown odd-over-even predominance. We found the abundance of PAH compounds with two to five rings in the sedimentary organic matter, in which PAH compounds with four or more rings have shown the highest abundance. The short (≤ nC21) and mid-chain (nC22-nC26) n-alkanes have shown a positive correlation with PAH abundance from study sites. This is likely the result of the combustion of terrestrial plant matter on the landscape at elevated temperatures (≥ 400 °C).

Occurrence and Distribution of Biomarkers in Loess-Paleosol Sequences of Tajikistan (Central Asia): Implication for Archaeo-Ecological Studies

Preprint

Mar 2024

Impact of farming on African landscapes

Article

Full-text available

Dec 2022

David K. Wright

As the continent with the deepest record of human history, the relationship between landscape formation and human subsistence practices is inseparable. The activities that constitute 'farming' are open for some matter of discussion, but essentially speak to the co-evolution of human, plant and animal reproductive systems along a continuum of interdependence. This process is ever evolving, but has resulted in the formation of landscapes in which anthropogenic processes characterize ecosystem functionality in nearly all biomes on the continent. Practices of cultivation, broadly conceptualized, across Africa are varied in the ways in which they have transformed ecological systems and landscapes. The use of fire as a landscape management tool dates to the Pleistocene, and penning of wild sheep to the early Holocene. The alteration of the landscape of fear by these types of human activities had fundamentally restructured trophic systems in Africa prior to the introduction of agriculture. However, the introduction of animal herding and intensive forms of plant cultivation by the middle Holocene correlated to even more significant ecological changes. The creation of agricultural landscapes has had a negative impact on biodiversity in some locations, whereas other some practices at different points in time have positively affected biodiversity. It is now recognized that humans have long influenced the evolution of landscapes wherever they live, but the current research focuses on where, when and how socio-ecological processes become coupled in the palaeoecological record.

Planetary-scale change to the biosphere signalled by global species translocations can be used to identify the Anthropocene

Article

Full-text available

Aug 2022
Palaeontology

We examine three distinctive biostratigraphic signatures of humans associated with hunting and gathering , landscape domestication and globalization. All three signatures have significant fossil records of regional importance that can be correlated interregionally and help describe the developing pattern of human expansion and appropriation of resources. While none have individual first or last appearances that provide a globally isochro-nous marker, all three signatures overlap stratigraphically, in that they are part of a continuum of change, with complex regional patterns. Here we show that during the later stages of globalization, late nineteenth to twentieth century records of species translocations can be used to build an interconnected web of palaeontological correlation with decadal or sub-decadal precision that dovetails with other stratigraphic markers for the Anthropocene. This palaeontological web is also a proxy for accelerating species extinction and of a state shift in the biosphere in the twentieth century.

European Trade in Malawi: The Glass Bead Evidence

Article

Full-text available

Aug 2022
Afr Archaeol Rev

In most African contexts, glass beads are evidence of direct and indirect exchanges between communities and are often useful chronological markers. Their analysis contributes to a better understanding of the social relationships between ancient societies. Over the last decade, the archaeometric analysis of glass beads has gained ground in Sub-Saharan Africa, but large regions across southeastern Africa have remained underexplored. Glass beads excavated from the Hora 1, Hora 5, and Mazinga 1 sites in the Kasitu Valley of the Mzimba District of northern Malawi were analyzed using laser ablation—inductively coupled plasma—mass spectrometry (LA-ICP- MS). These are granitic rock shelter sites located 40 km from Lake Malawi. They have predominantly Early Holocene and Pleistocene deposits but with a scattering of more recent material at the top. Analysis revealed that most of the beads were from European manufacture with one exception—a bead that has a composition typical of South Asia and that circulated from the fifteenth to the seventeenth century AD. Although Europeans were not present in the region before the second part of the nineteenth century, the presence of European beads testifies to trade directly or indirectly involving Europeans, most likely in association with increased trade in ivory and enslaved persons. The presence of the bead from South Asia and two cowrie beads from a fourth nearby site (Kadawonda 1) that dates to the seventh century AD show that European trade was the most recent manifestation of connections between the hinterland and the coast.

A collaborative agenda for archaeology and fire science

Article

Full-text available

May 2022
Nat. Ecol. Evol.

Humans have influenced global fire activity for millennia and will continue to do so into the future. Given the long-term interaction between humans and fire, we propose a collaborative research agenda linking archaeology and fire science that emphasizes the socioecological histories and consequences of anthropogenic fire in the development of fire management strategies today.

Ancient DNA and deep population structure in sub-Saharan African foragers

Article

Full-text available

Mar 2022
NATURE

Multiple lines of genetic and archaeological evidence suggest that there were major demographic changes in the terminal Late Pleistocene epoch and early Holocene epoch of sub-Saharan Africa1,2,3,4. Inferences about this period are challenging to make because demographic shifts in the past 5,000 years have obscured the structures of more ancient populations3,5. Here we present genome-wide ancient DNA data for six individuals from eastern and south-central Africa spanning the past approximately 18,000 years (doubling the time depth of sub-Saharan African ancient DNA), increase the data quality for 15 previously published ancient individuals and analyse these alongside data from 13 other published ancient individuals. The ancestry of the individuals in our study area can be modelled as a geographically structured mixture of three highly divergent source populations, probably reflecting Pleistocene interactions around 80–20 thousand years ago, including deeply diverged eastern and southern African lineages, plus a previously unappreciated ubiquitous distribution of ancestry that occurs in highest proportion today in central African rainforest hunter-gatherers. Once established, this structure remained highly stable, with limited long-range gene flow. These results provide a new line of genetic evidence in support of hypotheses that have emerged from archaeological analyses but remain contested, suggesting increasing regionalization at the end of the Pleistocene epoch.

A 1 km global cropland dataset from 10 000 BCE to 2100 CE

Article

Full-text available

Nov 2021

Cropland greatly impacts food security, energy supply, biodiversity, biogeochemical cycling, and climate change. Accurately and systematically understanding the effects of agricultural activities requires cropland spatial information with high resolution and a long time span. In this study, the first 1 km resolution global cropland proportion dataset for 10 000 BCE–2100 CE was produced. With the cropland map initialized in 2010 CE, we first harmonized the cropland demands extracted from the History Database of the Global Environment 3.2 (HYDE 3.2) and the Land-Use Harmonization 2 (LUH2) datasets and then spatially allocated the demands based on the combination of cropland suitability, kernel density, and other constraints. According to our maps, cropland originated from several independent centers and gradually spread to other regions, influenced by some important historical events. The spatial patterns of future cropland change differ in various scenarios due to the different socioeconomic pathways and mitigation levels. The global cropland area generally shows an increasing trend over the past years, from 0×106km2 in 10 000 BCE to 2.8×106km2 in 1500 CE, 6.2×106km2 in 1850 CE, and 16.4×106km2 in 2010 CE. It then follows diverse trajectories under future scenarios, with the growth rate ranging from 16.4 % to 82.4 % between 2010 CE and 2100 CE. There are large area disparities among different geographical regions. The mapping result coincides well with widely used datasets at present in both distribution pattern and total amount. With improved spatial resolution, our maps can better capture the cropland distribution details and spatial heterogeneity. The spatiotemporally continuous and conceptually consistent global cropland dataset serves as a more comprehensive alternative for long-term earth system simulations and other precise analyses. The flexible and efficient harmonization and downscaling framework can be applied to specific regions or extended to other land use and cover types through the adjustable parameters and open model structure. The 1 km global cropland maps are available at 10.5281/zenodo.5105689 (Cao et al., 2021a).

Past abrupt changes, tipping points and cascading impacts in the Earth system

Article

Full-text available

Jul 2021
NAT GEOSCI

The geological record shows that abrupt changes in the Earth system can occur on timescales short enough to challenge the capacity of human societies to adapt to environmental pressures. In many cases, abrupt changes arise from slow changes in one component of the Earth system that eventually pass a critical threshold, or tipping point, after which impacts cascade through coupled climate–ecological–social systems. The chance of detecting abrupt changes and tipping points increases with the length of observations. The geological record provides the only long-term information we have on the conditions and processes that can drive physical, ecological and social systems into new states or organizational structures that may be irreversible within human time frames. Here, we use well-documented abrupt changes of the past 30 kyr to illustrate how their impacts cascade through the Earth system. We review useful indicators of upcoming abrupt changes, or early warning signals, and provide a perspective on the contributions of palaeoclimate science to the understanding of abrupt changes in the Earth system. A synthesis of intervals of rapid climatic change evident in the geological record reveals some of the Earth system processes and tipping points that could lead to similar events in the future.

Early human impacts and ecosystem reorganization in southern-central Africa

Article

Full-text available

May 2021

Modern Homo sapiens engage in substantial ecosystem modification, but it is difficult to detect the origins or early consequences of these behaviors. Archaeological, geochronological, geomorphological, and paleoenviron-mental data from northern Malawi document a changing relationship between forager presence, ecosystem organization, and alluvial fan formation in the Late Pleistocene. Dense concentrations of Middle Stone Age artifacts and alluvial fan systems formed after ca. 92 thousand years ago, within a paleoecological context with no analog in the preceding half-million-year record. Archaeological data and principal coordinates analysis indicate that early anthropogenic fire relaxed seasonal constraints on ignitions, influencing vegetation composition and erosion. This operated in tandem with climate-driven changes in precipitation to culminate in an ecological transition to an early, pre-agricultural anthropogenic landscape.

Whole-genome sequencing reveals a complex African population demographic history and signatures of local adaptation

Article

Mar 2023
CELL

We conduct high coverage (>30×) whole-genome sequencing of 180 individuals from 12 indigenous African populations. We identify millions of unreported variants, many predicted to be functionally important. We observe that the ancestors of southern African San and central African rainforest hunter-gatherers (RHG) diverged from other populations >200 kya and maintained a large effective population size. We observe evidence for ancient population structure in Africa and for multiple introgression events from "ghost" populations with highly diverged genetic lineages. Although currently geographically isolated, we observe evidence for gene flow between eastern and southern Khoesan-speaking hunter-gatherer populations lasting until ∼12 kya. We identify signatures of local adaptation for traits related to skin color, immune response, height, and metabolic processes. We identify a positively selected variant in the lightly pigmented San that influences pigmentation in vitro by regulating the enhancer activity and gene expression of PDPK1.

The influence of ancient herders on soil development at Luxmanda, Mbulu Plateau, Tanzania

Article

Sep 2021
CATENA

In eastern Africa, ecologists have found that when mobile pastoralists abandon their temporary encampments, the accumulation of burned animal dung, wood, and other organic waste enriches the concentration of nutrients (e.g., calcium, phosphorous, magnesium) essential to soil health, in comparison to other soils without prior human habitation. These nutrient-enriched soils promote glade development and greater biodiversity. Geoarchaeological research on the time depth of this anthropogenic “nutrient hotspot” phenomenon has demonstrated that soils at several archaeological sites in southern Kenya still remain enriched in these soil macro- and micro- nutrients after several thousand years. However, soil scientists and geoarchaeologists do not yet understand how these anthropogenic soils vary over the extensive geographic conditions of eastern Africa. The discovery of a Pastoral Neolithic site (ca. 3000 BP) at Luxmanda on the Mbulu Plateau, Tanzania, provides an opportunity to examine if similar patterns of nutrient enrichment can be detected in a different geological and climatic zone. In this paper, we use geochemical and sedimentary analyses to determine how archaeological soils at Luxmanda differ from adjacent off-site soils and known archaeological soils in Kenya, as well as from computationally derived soil nutrient models for eastern Africa. Our results indicate that soils derived from anthropogenic sediments and ashy dung are 4 to 16-fold more abundant in soil macro nutrients relative to off-site or modeled values. This pattern fits previous studies’ observations that elevated macro- and micro-nutrients in soils are strongly correlated with ancient pastoralist habitation sites. We conclude that anthropogenic soils found at Pastoral Neolithic archaeological sites may be a valuable, but unappreciated, soil resource in eastern Africa.

Palaeoenvironmental data indicate late quaternary anthropogenic impacts on vegetation and landscapes in Mzimba, northern Malawi

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