Esther Jansma

Copepods link quahog growth to climate

From samples collected in 1983, 1991 and 2000, a long-term growth record for the bivalve Arctica islandica from the northern North Sea was constructed with methods derived from dendrochronology. Subsequent response-function analyses demonstrated that shell growth was mainly influenced by the abundance of copepods as recorded by the CPR survey. In years with dense copepod populations a major part of the downward flux of food particles is intercepted by the copepods before it reaches the seafloor. This may lead to a shortage of food for A. islandica resulting in a depression of shell growth. Although the abundance of copepods in the northern North Sea is linked to climate there is only a weak statistical relation between shell growth and climate.

TRiCYCLE: a universal conversion tool for digital tree-ring data

Abstract There are at least 21 dendro-data formats used in dendrochronology laboratories around the world. Many of these formats are read by a limited number of programs, thereby inhibiting collaboration, limiting critical review of analyses, and risking the long-term accessibility of datasets. Some of the older formats are supported by a single program and are falling into disuse, opening the risk for data to become obsolete and unreadable. These formats also have a variety of flaws, including but not limited to no accurate method for denoting measuring units, little or no metadata support, lack of support for variables other than whole ring widths (e.g. earlywood/latewood widths, ratios and density). The proposed long-term solution is the adoption of a universal data standard such as the Tree-Ring Data Standard (TRiDaS). In the short and medium term, however, a tool is required that is capable of converting not only back and forth to this standard, but between any of the existing formats in use today. Such a tool is also required to provide continued access to data archived in obscure formats. This paper describes TRiCYCLE, a new application that does just this. TRiCYCLE is an open-source, cross-platform, desktop application for the conversion of the most commonly used data formats. Two open source Java libraries upon which TRiCYCLE depends are also described. These libraries can be used by developers to implement support for all data formats within their own applications.

Route persistence. Modelling and quantifying historical route-network stability from the Roman period to early-modern times (AD 100–1600): a case study from the Netherlands

Research on route-network stability is rare. In time, due to cultural and/or natural causes, settlement locations and route orientation shift. The nature of these spatial changes sheds light on the complex interaction between settlements and surrounding natural landscape conditions. This study investigates the stability of route networks in the Netherlands during the past two millennia by determining their persistence through time. Environmental, archaeological and historical data are used to reconstruct and compare route networks. By using network friction, archaeological data on settlement patterns and route networks in combination with historical data (e.g. old maps), we were able to model route-network persistence (not necessarily continuity) from the Roman to early medieval periods (AD 100–800) and from the Early Middle Ages to the Early Modern Times (AD 800–1600). Results show that around 67.6% of the modelled early-medieval routes in the Netherlands are persistent with routes in the Roman period. Covering a much larger surface area of the Netherlands, 24.5% of the early-modern routes show a clear persistence with their early-medieval counterparts. Besides the differences in surface area, this downfall can largely be explained by cultural dynamics, with 71.4% of the early-modern route network following modelled movement corridors already in existence during the Early Middle Ages.