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ABSTRACTStone and earthen architecture is nearly ubiquitous in the archaeological record of Pacific islands. The construction of this architecture is tied to a range of socio-political processes, and the temporal patterning of these features is useful for understanding the rate at which populations grew, innovation occurred, and social inequality emerged. Unfortunately, this temporal patterning is poorly understood for many areas of the region, including the Sāmoan archipelago. Here, we describe a project directed toward establishing a robust chronology for the construction of these earthen and stone terraces and linear mounds on Ta‘ū Island. Using recent methodological improvements, we highlight the tempo at which different architectural types were constructed on the island and the implications for understanding demographic expansion and changing land tenure practices in the last 1500 years. This research suggests the construction of architecture was largely confined to the 2nd millennium AD with a small number of terraces plausibly built in the 1st millennium AD. This temporal patterning suggests that a reconfiguration of settlement patterns occurred within West Polynesia as people there moved into other regions of Oceania.

Meteoric beryllium‐10 (10Bem, t1/2= 1.4 Myr) is a cosmogenic radionuclide that remains largely underutilized for deriving hillslope‐scale estimates of erosion on uplands under conditions of land use change. We applied two different models for estimating erosion rates from observed 10Bemconcentrations (a one‐dimensional model predicting vertical profiles of 10Bemwithin hillslope soils [loss only, diffusion only, LODO] and a two‐dimensional model predicting the concurrent evolution of hillslope topography and 10Bemdistributions via bioturbation, chemical mobility, and surface erosion [Be2D]). Both models were used to derive pre‐European and post‐European settlement erosion rates (Enatand Epost, respectively) across paired cultivated and uncultivated hillslopes in west‐central Minnesota, USA. Epostestimates from 10Bemwere compared to Epostestimates derived from 137Cs inventories and the process‐based Water and Tillage Erosion Model (WaTEM). The results from these models suggest that erosion rates from upper positions on the cultivated hillslope have increased from an average of 0.047 mm/year under natural conditions to Epostvalues of 3.09 mm/year. The Be2D and LODO models, on average, produced Epostestimates that were similar in magnitude to WaTEM and 137Cs conversion models. This numerical convergence does not imply absolute 10Bemmodel accuracy, particularly when considering the uncertainties inherent in each approach, but it does suggest that the orders of magnitude increase in estimated erosion rates from Enatto Epostis robust. Additionally, the pattern of Epostestimates produced using 10Bemconversion models is supported by the distribution of soil inorganic carbon at the study site. Our results demonstrate that 10Bemcan provide reasonable estimates of both predisturbance and postdisturbance erosion rates in landscapes that have undergone extensive human modification. Agricultural practices have substantially changed soil erosion rates in the Midwestern United States. Although much work has been devoted to understanding the changes in soil erosion rates with land cover change, the ability to quantify those changes at discrete locations on the landscape over long periods of time has been limited. We use a set of tracers and models to estimate presettlement and postsettlement erosion rates on a hillslope in west‐central Minnesota, USA, and show that soil erosion has increased by approximately 1 to 2 orders of magnitude over a period of approximately 110 years. This has implications for how we view our current agricultural landscapes and how we think about soil sustainability in the future. Meteoric beryllium‐10 is used to generate point‐based estimates of long‐term erosion on paired hillslopesThese estimates suggest that erosion rates have increased by 2 orders of magnitude under agricultural managementModel choice influences erosion rate magnitude, but average rates are similar to estimates from process‐based models and cesium‐137

Erosion rates dictate the morphology of landscapes, and therefore quantifying them is a critical part of many geomorphic studies. Methods to directly measure erosion rates are expensive and time consuming, whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents. If hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates. In this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high‐resolution (1 m) digital elevation data. Published and new cosmogenic radionuclide analyses in the Feather River basin, California, suggest that erosion rates vary by over an order of magnitude (10 to 250 mm kyr−1). Hilltop curvature increases with erosion rates, allowing calibration of the hillslope sediment transport coefficient, which controls the relationship between gradient and sediment flux. Having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature. Additionally, we show that hilltop curvature continues to increase with rising erosion rates after gradient‐limited hillslopes have emerged. Hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient, providing soil production on hilltops can keep pace with erosion. Finally, hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels. Rapid erosion rates can be derived from high‐resolution topographyA technique has been developed to map hilltopsWe can give erosion rates at the scale of individual hillslopes for the first time

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Thawing of permafrost and a subsequent accelerated loss of mercury from the soil constitute a possible threat to the quality of high‐latitude surface waters. In this paper we estimate the export of mercury generated by a thawing palsa mire in northern Sweden, by assessing net mercury storage changes along thermokarst erosion gradients. Lower mercury inventories in inundated hummocks covered by water (≤3.1 mg Hg m−2) than in noneroding hummocks (between 5.5 and 8 mg Hg m−2) suggests a release of ∼40–95% of the mercury pool from hummock peat experiencing subsidence and submerging. The documented expansion of submerged areas between 1970 and 2000 in the studied system indicates that permafrost thawing has initiated a mobilization of 34 to 50 g mercury. We stress the need of further assessing the fate of this mercury because the size of the mobilized mercury pool might be highly significant for subarctic surface waters.