In the SW coast of Spain, the environmental changes and their effects in the landscape dynamics during the Holocene time intervals based on climatic fluctuations have attracted the interest of researchers for years . This interest is now specially high and associated to the knowledge of the fragile Atlantic landscapes and the role of the Guadalquivir basin within the Atlantic Ocean and the Mediterranean Sea.
The interrelationship between climate and the genesis of geomorphological processes has a singular importance in the paleogeographical research. Nevertheless, the reaction of river basins to climatic variations since the Flandrian interglacial transgression and the linkage to the human settlement patterns is an important research subject and still the matter of scientific debate.
Understanding the relationship between archaeological and geological datasets represents the main objective of the present project that has been developed in the common framework of Geology and Anthropology.
Climate trends and its variations have a powerful influence on human settlement patterns, migrations, technology adaptations, demographic evolution, etc… These aspects are the main reason of the rise, evolution and collapse of the civilizations.
The main objective of this work, through the application of geophysics survey techniques, remote observation and combined sampling procedures are the assessment, characterization and mapping using a digital elevation model (DEM) to understand the paleochannels and fluvial landforms now submerged in the river basin of Huelva´s maritime province; and understand how these features, based in their typologies and distribution, can help understand the depositional systems in the paleoestuaries.
This kind of features provide most valuable natural archives of the information related to the coast, linked to the environmental changes that occur in the past, and also, they are the main areas where the human groups started to settle in and interact very closely with the environment. It is this environment the main resource for these human communities and their societies.
The evaluation of ancient landscapes and the paleogeographic reconstructions play an important role in the archaeological interpretation, by providing the essential physical background that helps understand the conformation of past societies.
Researching paleo-geographic environments like the Gulf of Cádiz is relevant to improve our understanding of the influence that the vicinity of the sea, river basins and associated processes. had on people that settled this area, his organization and also provided to the area a key role in the eventual land and sea transportation routes in the past.
During the Last Glacial Maximum (LGM), the position of coastlines and all the water courses related, such as alluvial deposits or soil configurations, have strongly influenced the location of community settlements and consequently the strategic and logistic community actions as far as they were able to develop the technology to maximize the advantages provided by the surrounding environment.
The scientific ability to undertake paleo-geographic reconstructions and the access to the archaeological records of buried paleolandsurfaces that were part of the human habitat is relevant for prehistoric archaeology in general and particularly for Mesolithic archaeology in SW Spain coast.
The hypothesis of the present project tackles the dynamic relationship between the adaptation of human groups and the variations and transformations of the relevant riverine, estuarine and coastal landscape changes since this relevant landscapes were selected by human groups and at the same time were transformed by Pleistocene and Holocene sea-level changes .
Through geophysical and archaeological datasets, we could identify the gradual change that was generated by the Flandrian interglacial transgression. By identifying climate variations and changes in human settlement patterns we can also identify fluctuations of these changes and determine how changes favored or reduced the available resources of these communities.
From the point of view of Archaeology, the variations on the lithic industries in the archaeological sites in the area of the Gulf of Cadiz that right now may lie underwater, raise basic questions about the culture linked to this type of industries; we need to unravel if they were the result of technology due the available feedstock provided by the environment, the local technology tradition or the necessary adaptations based in the succession changes that occured in the environment and the landscape.
For the Mesolithic period in SW Spain, the available archaeological dataset is a valuable starting point for this study, but the knowledge of the human settlements, now submerged and bounded to the complete paleo-channels landscape (rivers, estuary and coast), we believe that it represents a key perspective to the interpretation of past human actions/strategies within the landscape context.
If we study communities associated with a model of settlement adaptive and mobile, they normally apply versatility and adaptability in the technology to gather food and keep the internal cohesion, this fact has been proved also in the diet evaluation and patterns from the early homo.
We now that the Mesolithic time span may vary in different parts of Eurasia and the origin of migrations are subject to an interesting debate. Some authors deal with declining marine productivity in coastal areas and some other with a proposed shift to drier, more continental conditions across north-west Europe. In a wider and general perspective, the technological tradition was forged in an environment subject to transformation, and also identifying patterns of deliberate disturbance of the environment by Mesolithic foragers, as part of a conscious land-use strategy designed, for example, to attract ungulate populations to the disturbed areas and increase hunting efficiency. The same impact, technology and diet evolution are identifiable on coastal environments where we clearly are able to identify the changes in the abundance of species as the result from the impact of human foraging on the populations of mollusks and rocky-shore intertidal mollusks that normally, due the accessibility, were exploited intensively and frequently.
The determination of the Mesolithic communities migration or settlements patterns in Eurasia were mainly determined by short and long distance population movements, seen as fundamental mechanisms for the formation and distribution of regional archaeological cultures from the Paleolithic to historical periods. The main hypothesis in this study supports that this information is identifiable in the submerged settlements of the Gulf of Cádiz associated to the paleo-environment characteristics and as we believe that the identification of this settlements is a primary social response to environmental, demographic, and livelihood pressures. We believe that the underwater archaeological record of the paleo-landscape of the Gulf of Cádiz is the result of complex local and regional evolution, interaction, exchange, and cultural exchange with North Africa communities and the ancient Levant, reinvigorating essential debates around migration, diffusion, and autochthonous change in Spanish prehistory and also in the historical-chronological outlook debate of the archaeological sites associated to the Gulf of Cadiz.
We believe that transformations, landscape adaptations and technology were an all pervasive aspects of Mesolithic life. Although archaeologically we have tended to focus on a small subset of these; often at a comparatively large scale, and still related to old academic ideas that we believe that must be revised, mainly related to ideas about evolution and progress, especially in the concept of the initial complex hunter-gatherers societies.
It has been proven that the Mesolithic is highly variable as an archaeological phenomenon. Many aspects of that variability reflect genuine differences in the past, generating cultures that highlight technology complexity or commercial networks. Likewise due to physiographical characteristics or their cultural tradition it is believed that the paleo-landscape of the Gulf of Cadiz hosted a society tributary of the Mesolithic culture that emerged on the history necessarily trought the power of the myth and the ancient geographical descriptions.
Our initial proposal is to determine the paleo-riverbeds of the rivers Guadiana, Piedras, Tinto, Odiel and Guadalquivir developing a DEM (Digital Elevation Model) using the most common single-direction method, the D8 algorithm, that has been tested in several academic studies with success.
Implement side scan sonar mosaics and derived sea floor characterization
Implement chirp survey and potential paleo-channel identification
Identify visual features using ROV and scientific dive operations
The following phases are defined to develop the method:
STEP 1: To compile the input data for our model: where the bathymetric data for the Gulf of Cádiz are available, the source is the nautical charts and databases from the Instituto Hidrográfico Nacional . These dataset plus other complementary are introduced to a digital elevation model (DEM) of the seafloor. We should keep in mind that the soundings of the Instituto Hidrográfico Nacional nautical charts normally have a separation of 15 seconds latitude and longitude. That initial stage defines the contour plot of the input data for the Gulf of Cadiz in the area of the maritime province of Huelva. We defined that the area between the coast and the low water mark of minimum tides outwards up to 70 meters isobath is the study area of this project.
STEP 2: The second stage of the development of the DEM is to remove the pits (depressions) in the model. The objective is to ensure that small depressions, which exist due to processing errors, so that they do not influence the final calculation of the river DEM network. Also, in this stage we decide to interpolate or not small scale bathymetry datasets from other studies or projects available that could improve our model along the entire area or just in selected sectors, that include our proper sourced datasets.
STEP 3: Define the Flow Direction Grid (FDG) of the DEM. This procedure determines the flow direction of each DEM element, basically taking in consideration the direction in which the water would have flown out from that element. The direction is determined by the orientation of the element; this model was developed and presented in other projects successfully.
STEP 4: Calculating the Flow Accumulation Grid (FAG) from the FDG, We will follow the procedures of filling every cell of the DEM with the cumulative number of cells that flow into it. The step number 3 will help to define the cells that flow into the target cells.
STEP 5: Identify in the model, the potential areas (depressions) that we were not able to be solved in step 1. We will try to identify potential depressions that could occur from digitalization errors. In this step we should identify clearly depressions from the application of the method or depressions defined by water accumulation around the sinkhole, from which the paleo-river continued its course. •We think that this is the basic procedure for the initial definition of the DEM, but after the successful definition of the DEM, we would like to surpass the initial limitations of this method.
As stated at the beginning of this section, the regular resolution of the DEM obtained using the nautical charts of the Instituto Hidrográfico Nacional is 15 seconds which is about 350 meters, this resolution maybe is valid for some hydrographical analysis but it´s coarse for the potential identification of small gorges or narrow features carved eventually by the paleo-rivers in the terrain, mainly if this features has been filled with sediment.
We would like to improve the system applying additional techniques:
Side Scan Sonar • The Side Scan Sonar is a device used to obtain and using the specific software treat images of marine and continental seabed water bodies. These images are the result of the application of exploration techniques to locate study and interpret outcrops of submerged substrate where it may be possible to identify features, items or human settlements of historical value. In this project, the role of the Side Scan Sonar is aimed at obtaining datasets which can provide a wide range of scientific evidence related to geological facies, sediment patterns and mainly allow us the localization and spatial contextualization of items on the surface, improving the information derived from the DEM. The side scan sonar will be used to survey the polygon defined area and to obtain a supportive bathymetric map, we will call this document as “physical map”. Using DGPS measurements, the physical map of the seabed will be endowed with a geographic coordinate system. Accuracy in localizing features are of about 1m. The geo-referenced physical map has to be considered as a support to the DEM on which additional information will be plotted and integrated in a GIS.
Seismic survey •Chirp sub-bottom profilers produce high-resolution images of the near-surface. An attribute of the sea-bed reflection in chirp data are fluctuations in polarity between adjacent traces. Two analyses are valuable for the identification of the features that we would like to identify under the seabed: the first incorporates changes in an acoustic impedance gradient directly over the seabed; the second uses changes in the thickness of the uppermost sediment layer. Mixing of adjacent traces produces a consistent polarity for the sea-bed reflector, generating contrast patterns among different reflections coefficients. •Reflection coefficients are calculated, using amplitude information derived from single-traces and polarity information from trace mixing. This system could provide valuable data for the identification of sectors and micro spatial sectors of the buried or sediment filled paleochannels that could supply relevant data related to potential archaeological sites. The seismic survey method is fully compatible with side scan sonar survey tracks that provide surface information, so we will optimize the survey using both methods (Side scan sonar and seismic survey) combined during the tracks of the scientific cruise. The application of the seismic survey allows us to generate three dimensional seismic-reflection images of the layers patterns under the seabed. Shallow seismic reflection can provide coherent high resolution images of thin, alternating sand and clay sequences in many shallow water environments that generate a coherent context for the potential identification of human settlements linked.
ROV •New technologies allow archaeologists to explore the human past in the depths of the water bodies far beyond the depth boundary set by the scuba diving. Using robots and advanced sensors originally developed for other applications, social scientists adapted the deep water technologies for their scientific research. Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs) allow archaeologists to survey the sea floor, these increases dramatically the number of underwater sites available for archaeological study. Several projects in the past years in the Mediterranean and the Black Sea have proven the scientific merit of archaeology in deep water. I have proven expertise in the use of ROV in deep water archaeological surveys during the last ten years. We are full ready for the development of this project to implement the procedures and methodology employed in the fieldwork at sea for gathering data from submerged sites of archaeological interest. The emphasis in this activity applied to this work simplify the archaeological work by employing unmanned robotic vehicles and automatic procedures and protocols that can be applied to deep water sites that are not reachable by divers. Conducting an archaeological ROV project to acceptable archaeological standards requires extensive planning and combined techniques. High-resolution geophysical survey data must be a part of this planning process as described previously in the present theoretical framework for the project.