Potential zone for photosynthesis in natural waters is restricted to a relatively thin illuminated surface water layer. The thickness of this layer is often indirectly estimated by measuring the depth in which 1% of the photosynthetically active radiation entering the water remains. This depth is referred to as the euphotic depth. A coarser way to evaluate the underwater light penetration is to measure the Secchi depth, which is a visual measure of water transparency. The numerical relationship between these two optical parameters, i.e., conversion coefficient m, varies according to the changes in the optical properties of water, especially in transitional coastal waters. The aim of our study is to assess which is the most suitable criterion to base these coefficients on. We tested nine methods, seven of which were locally calibrated with our own in situ data from the optically heterogeneous Baltic Sea archipelago coast of SW Finland. We managed to significantly improve the accuracy of modeling euphotic depths from Secchi depths by using scalable and locally calibrated methods instead of a single fixed coefficient. The best results were achieved by using methods, either continuous functions or series of constants, which are based on water transparency values.

The role of open spatial data is growing in human-history research. Spatiality can be utilized to bring together and seamlessly examine data describing multiple aspects of human beings and their environment. Web-based spatial data platforms can create equal opportunities to view and access these data. In this paper, we aim at advancing the development of user-friendly spatial data platforms for multidisciplinary research. We conceptualize the building process of such a platform by systematically reviewing a diverse sample of historical spatial data platforms and by piloting a user-centered design process of a multidisciplinary spatial data platform. We outline (1) the expertise needed in organizing multidisciplinary spatial data sharing, (2) data types that platforms should be able to handle, (3) the most useful platform functionalities, and (4) the design process itself. We recommend that the initiative and subject expertise should come from the end-users, i.e., scholars of human history, and all key end-user types should be involved in the design process. We also highlight the importance of geographic expertise in the process, an important link between subject, spatial and technical viewpoints, for reaching a common understanding and common terminology. Based on the analyses, we identify key development goals for spatial data platforms, including full layer management functionalities. Moreover, we identify the main roles in the user-centered design process, main user types and suggest good practices including a multimodal design workshop.

We measured depth profiles of underwater PAR (photosynthetically active radiation) together with optically derived turbidity and chlorophyll fluorescence values at 11 sampling stations in the South-West Finnish archipelago of the Baltic Sea. The data were collected eight times during the spring, summer and early autumn of 2010. The results illustrate complex and multidimensional variations in the euphotic depth, which was subject to fourfold and twofold differences in the geographical and seasonal dimensions respectively. The spatio-temporal inconsistency and non-linearity of the seasonal euphotic depth variation calls for further studies at different spatial and temporal scales

Our paper aims at advancing global change management in marine archipelago environments. Water properties vary along temporal and vertical gradients, and studies indicate that these patterns may be site-specific, i.e., they may vary at local or regional scales. Understanding these complex processes is crucial for designing environmental monitoring campaigns or assessing the scalability of their results. To our knowledge, the four-dimensional (temporal, vertical and horizontal) patterns of water quality have not been statistically quantified. In this paper, we partition the variation in four key water property variables into temporal, vertical and horizontal dimensions, by utilising a unique pre-existing high-density dataset and multilevel regression modelling. The dataset comprised measurements of temperature, salinity, pH and chlorophyll-a concentration, sampled eight times from April to October on the SW Finnish archipelago coast. All variables were sampled along the depth gradient and at local (10² m) and regional scales (10⁴ m) at 20 sites. All measured variables varied significantly along the temporal and vertical gradients, and the overall levels, temporal patterns and vertical gradients of these variables were significantly site-dependent. Our study confirms that many water properties, especially chlorophyll-a concentration, show high four-dimensional variability in the complex archipelago environment. Thus, studies on the regional dynamics of archipelago water properties call for a high sampling density in time, along the vertical gradient, and in space.

Contributing to multidisciplinary studies of human population history, this paper presents an analysis chain to comprehensively model the historical travel environment in Finland, based on a study of spatial patterns of overall accessibility within the country. We created a spatial historical travel environment model over the whole country using high-quality terrain and landscape spatial data, combined with information from historical sources that characterize the landscape in terms of travel effort given the environmental and human-related factors current up until the late 19th century. Spatial analyses of historical travel effort based on the travel environment model indicate travel speeds for different parts of the country, ranging from 0.6 to 5.3 km/h. This is nearly a tenfold range, potentially highly significant for studies relying on historical travel effort and contacts between population groups in Finland. The results show that the overall travel effort in southern Finland is significantly smaller than in the north: almost all areas in southern Finland have average travel speeds above 3 km/h, whereas the average travel speeds below 2.5 km/h are typical in the north. A more detailed study using random 100 km transects highlights the variability of the least-cost routes in different landscapes and between different source data combinations in each cost surface. The paper identifies great potential in combining the existing spatial data archives with archaeological, linguistic, and genetic data in a GIS analysis, to study the travel effort and its impact on the observed spatial patterns of languages, genetic traits, and archaeological findings.