Insular-Arc Volcanic Ecosystems as Centres of Forming the New Parts of Continental Biosphere (by the example of South-Kuril Insular Ridge) 111
Citation: Insular-Arc Volcanic Ecosystems as Centres of Forming the New Parts of Continental Biosphere(by the example of South-Kuril Insular Ridge). American Research Journal of Earth Science; V1, I1; pp: 1-43
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The empirical statistical models of the island-arc stage of continental biosphere development in the North-West Pacific have been created by the example of regional bioclimatic system and experimental testsite near the active Mendeleev Volcano on the Kunashir Island (the South Kuril Ridge). The causal mechanisms of the known geographical phenomenon of insular extratropical Neo-Pacific, i.e., the general descent of the boundaries of altitudinal bioclimatic zones and the southward shift of natural zones on islands compared to the neighboring continents, are discussed. The phenomenal feature of bioclimatic system at the stage of insular landscape formation is the direct subordination of phytobiota to vertical hydrothermal gradients. It forms a system of future altitudinal zonality of the continent already within a frame-work of low-mountain island-arc landscape.It was shown that on this stage local geomorphological conditions created the centers of origin of diverse phytocoenological and soil structures of the higher (zonal-regional) levelat the initial stages of continental biosphere development.
An exceptionally important backbone role of forest phytobiota in the establishment and development of young volcanic landscapes was demonstrated. Theoptimizingstrategyprogramfor the development of plant communities, which is aimed at the maximum biomass formation on forest island-arc landscapes, is much more marked compared to their zonal analogs on the neighboring continent. At the same time, an exceptionally high percentage of green mass in the structure of production results in the acceleration of biological cycle as a factor of stability of forest community. All the above ensures the survival of insular ecosystems of the boreal Neo-Pacific under unfavorable conditions of “cold” oceanicity.
It was determined empirically that the structure and function oftopogeo(eco)systems in mobile belts of the planet are the sources of evolutionary global biosphere processes and driving forces of the biosphere evolution in whole.
Keywords: Pacific ocean mobile belt, regional bioclimatic system, altitudinal-expositional zo-nation,insular volcanic landscape,forest ecosystems, structure and functioning, empirical-statistical modeling
Kuril Ridge is the part of the Pacific Ocean oro-climatic mega ecotone of Northern Eurasia which covers the eastern, tectonically active margin of the continent and the insular land within the temperate and sub-Arctic geographic belts . This transition zone is characterized by the submeridional extension of morphostructural belts of different ages and the marked latitudinal and longitudinal-sectoral differentiation of the climate. It is part of the global belt of convergence of matter-energy fluxes on the Earth surface: the so-called mobile belt of the planet . The interaction between and transmutation of the two main types of geographical environment (oceanic and continental) in this “continental-oceanic suture zone” is extremely dynamic ; therefore, the insular, peninsular and littoral-continental territories (as well as the coupled shelf areas) are a natural laboratory for studying the modern geological stage of biosphere development, since this stage is most marked exactly in the Pacific mobile belt.
According to V. B. Sochava , island-ark territoryof Kuril Ridge includes in Cenozoic volcanogenic Neo-Pacific whichis replaced to the West by Sub-Pacific, i.e., the marginal continental geographical space of the Mesozoic geological age, and after that – by much more ancient (Paleozoic) Paleo-Pacificbeing part of the Siberian platform. Island-ark volcanic arcs are the initial stages of continental biosphere development, where centers of origin of diverse phytocoenological and landscape structures of continental type are created.
Pacific mega-ecotone of Northern Eurasia shows up one of sources of continental biosphere forming beginning in middle of Mesozoic . Next processes created necessary conditions for that: (a) the frequently repeated joining and isolation of insular and marginal-continental land, which caused periodic isolation of biocoenotic complexes and interchange between them; it accelerated the evolutionary development of plant and animal populations and contributed to the diversity of their modern adaptations; and (b) intensive orogenesis and volcanism, which created the primary altitudinal differentiation of biota on the mountainous islands of the PacificOcean. Ecological niches remained permanently vacant, with the migration of modifications of biotic communities from the neighboring altitudinalzones. The primary altitudinal-zonal groupings of organisms and ecosystems were a basis of formation of the zonal types of geographic environment on the plains of all continents. These are some of the basic points of the concept of evolutionary biogeography put forward by D.V. Panfilov .
The problem of oceanicity and continentality has not yet been sufficiently developed for the eastern margin of the Asian continent, including the insular and peninsular territories going far into the water area of the Pacific Ocean and its marginal seas. For example, the causal mechanisms of two geographical phenomena of extratropical Neo Pacific: the general lowering of the boundaries of altitudinal climatic belts on the islands and the southward shift of natural zones compared to the neighboring continent, are still unclear [37, 38, 58, 90, etc.]. The role of climatic parameters and heat balance structure per se in the formation of sharp biogeographical differences between the insular-arc Neo Pacific and the marginal-continental and continental-insular Sub Pacific has not been revealed either.
This presentation is aimed to elucidate some of the most substantial, in our opinion, peculiarities of spatial structure of the regional bioclimatic system of the Kuril Insular Arc (within the boreal belt), as well as to assess the creative role of this system at the insular-arc geological stage of evolution of the continental biosphere. The regional hydrometeorological data on the South Kuril Islandswere used for bioclimatic analysis. The empirical statistical models of the island-arc stage of continental biosphere development in the North-West Pacific have been created by the example of experimental testingsite in the vicinity of the active Mendeleev Volcano on the Kunashir Island (the South Kuril Ridge).Here (near by Yuzhno-Kurilsk weather station) in August, 1985 large-scape landscape-ecological survey was performed at experimental test site (Figure 1).
Staying for a long time under the conditions of monsoon-oceanic climate, the plant cover of the temperature belt on the island and marginal continental sectors of Pacific Mega ecotone of Northern Eurasia developed continuously . The transition of flora and vegetation from the tertiary to quaternary period was relatively smooth, with migration of individual elements of the tertiary flora from north to south and back and with intrusion of representatives of the cold climate .
The processes of the primary subaerial biogenesis occurring at the Pacific Ring of Fire (the mobile belt of the Earth) are the successive stages of modern increment of the continental biosphere.The processes of formation of volcanogenic-accumulative morphosculpture created a lithogenic basis of the island-arc stage of establishment and development of the next part of the continental biosphere. All of the newly-formed terrestrial natural complexes in the oceanic mobile belts pass through this stage. Hence, the “Mendeleev Volcano” pilot test site on the Kunashir Island is undoubtedly representative for perceiving the initial stages of establishment and development of terrestrial geo(eco)systems in the surrounding oceanic environment.
Geomorphometry mapping was done by L.S. Sharaya. The legends to the geomorphological map, according to (Атлас …, 2009): Mountain landscapes. Volcanic relief. Denudation-volcanic (weakly destroyed): 1 – the craters and steep upper parts of the cones; 2 – middle mountains, low mountains; 3 – lava-pyroclastic plains, baja-das (foothill trails). Denudation-volcanic (strongly destroyed): 4 – the craters and upper parts of the cones; 5 – middle mountains, low mountains; 6 – lava-pyroclastic plains, bajadas (foothill trails). Erosion-denudation relief (denudation-tectonic): 7 – middle mountains; 8 – low moun-tains, mid-altitude hill country; 9 – low-altitude hill country. Plain landscapes: 10 – Pleistocene abrasion-accumulative plains. Other designations: 11 – goltsy; 12 – river valleys; 13 – lakes; 14 – warm sea currents.
VOLCANOGENIC BASIS OF THE INSULAR-ARC LANDSCAPES
Morphotectonics of the Kuril Island Arc
The Kuril Islands are included into the system of island arcs of the Pacific Ocean Mobile Belt. They are the above-water part of epigeosynclinal mountain ranges separating the kettle of the marginal Sea of Okhotsk from the Kuril-Kamchatka Trench in the Pacific Ocean. The island-arc systems are the zones of formation of the major geochemical reservoirs of our planet; therefore, they play the key role in plate tectonics , which creates the shape of continents. This very fact predetermines the representativeness of island-arc volcanic landscapes as objects for studying the initial stages of formation of the continental biosphere and disclosure of the initial mechanisms of subaerial landscape genesis.
Geological structures, according to : I – central cone; II – second somma; III – first som-ma; IV – nonsegmented mass (partly tertiary); V – foundation (tertiary terrigenic-pyroclastic rocks). Other designations: 1 – the outlines of ancient caldera; 2 – the outlines of young caldera; 3 – solfatare fields; 4 – pyroclastic flow; 5 – test grounds; 6 – test grounds with temperature anomalies in soil; 7 – the boundaries of geothermal fields of the volcanic cone, according to Sa-fonov et al., 1998); 8 – the line of seismic profiling (see below Fig. 5).
23, 30, 21, … – the numbers of sample plots (points).
According to the modern concepts , the Kuril Island Arc is a system of volcanic belts of different age, which are situated above the zones of subduction – the V-shaped underthrusting of oceanic crust beneath continental crust. Volcanoes form on large magmatic columns, or diapires, which rise in the asthenosphere in regular rows by means of gravitational convection (buoying). On the Kuril Islands, there are 104 active volcanoes, apart from submarine volcanoes; 39 of them are active . The effect of volcanism on the natural-territorial complexes of the island is directly proportional to the area and volume of volcanic bodies. Volcanic cones and adjacent lava and pyroclastic plains make up to 90% of the area and volume of all Kuril volcanic landscapes . The percentage of volcanic landscapes of the island area is as follows: Iturup – 35; Urup – 66; Simushir – 44; Shikotan – 79; Onekotan – 90; Paramushir – 28.
The present-day relief of the Kunashir Island is a chain of large and small volcanoes of different age (from middle-Pleistocene to present-day) connected with abrasion-accumulative lowland-plain vents. These vents emerged in the Late Holocene: 2200–2300 years ago . Geomorphometric processing of the satellite image of the Kunashir Island by L.S. Sharaya showed (Fig. 4.1 a) that this island was formed by the linear-nested arrangement of volcanoes typical of the Greater Kuril Ridge  on the basis of at least nine volcanic cones of different age (from Early Pleistocene to present-day) and, accordingly, different levels of activity. The most ancient volcanic cones compose the Dokuchayev Range, which is unreasonably indicated on the geomorphological map (Fig. 4.1 b) as an erosion-denudation (denudation-tectonic) relief, without any allusion to its originally volcanogenic genesis. Low-lying isthmuses combine the volcanic cones into a single island system of Kunashir.
Thus, in the mobile belt of the planet, volcanoes are the foci of accretion of the continental biosphere. The lithogenic basis of young island-arc landscapes is directly related to the deep endogenous processes in the “living planet” Earth, which determines the direct landscape-forming influence of the morphotectonic factor . The extremely high frequency and intensity of eruptions and tempos of relief formation (on the geological time scale) cause an exceptionally complete correspondence between the forms of the earth’s surface and the geological structure . Periodic recurrence of volcanic activity may bring to naught the results of denudation processes closely associated with the landscape formation.
The poorly developed denudation processes in the regions of present-day volcanism, as has already been said, are due to mainly tectonic downwarping (or delayed uplift) of these areas compared to the neighboring territories. Under such morphotectonic conditions, the destruction and ablation of bedrock layers proceed slowly, while the development of denudation-accumulative exogenous is considerably suppressed – largely due to the poorly developed river network of the territory. Hence, the predetermining role of volcanogenic-accumulative morphosculpture in landscape structure is much more marked.