Sea Level Forecast Indicators: Sea-Level Rise Forecast by “The Moon and Sun” Foraminifera Species Indicators

Abstract

Global Sea-Level Rise is caused by two main factors: thermal expansion (ocean water warms and expands), and the contribution from ice sheets (glaciers, land-based ice sheets, and sea ice) due to increased melting, and the continued increase in the twenty-first century is important in determining the distribution of species and habitats, and projections show that by 2100, thermal expansion and glacial melting are expected to cause a rise by 0.26 to 0.98 m, based on climate models, and considering high and low emissions scenarios. However, the contribution of the Greenland and West Antarctic ice sheets could increase these amounts. A potential analogue to modern greenhouse conditions is the climate of approximately five to three million years ago, in the early Pliocene epoch, which provides important clues where earth was in one of the warmest times showing the increase of hurricane pathways all over the world.

The increase in the sea level rate in the Anthropocene Epoch is to blame for higher temperatures. As temperature rises, water heats up and expands causing warming oceans to take up more space and invade land. Higher temperatures melt glaciers and ice caps faster, which in turn adds more water into the oceans. The higher water temperature is likely to increase extreme sea level events, like storm-driven waves, surges, tropical and extra tropical cyclones (also known as hurricanes and typhoons), which have become nearly three times more intense and frequent during the twentieth century. More frequent and stronger hurricanes imply greater heating of water parcels, with consequent warmer temperatures in the tropics, and in turn, more hurricanes.

The total rise of sea level from 1901 to 2010 is larger than the average rate during the previous 2000 years of 19 cm, with global average sea level trends showing an increase by 0.18 cm per year, and the Intergovernmental Panel on Climate Change forecasts that global sea levels will rise by around 47 to 62 cm by 2080.

Foraminiferal assemblages indicate the differences in ocean levels from past to present with the establishment of species zonation occupying marshes, bays, lagoons, reefs, and deep-water marine environments. The rather narrow and accurate sensitivity to limiting factors make Forams “the markers of the sun and the moon” in time and space, and paleo deposits related to paleo-sea level in all ecosystems around the world. Likewise, they forecast future changes and impacts, allowing us to give recommendations to mitigate and remediate effects.

Photo Symbiont-bearing large benthic Foraminifera (LBF) species with zooxanthellae algae which dwells in reef areas needs the sun’s proximity under the water to flourish, therefore, light is a limiting factor for such organisms, because these symbionts need to be able to photosynthesize.

The sun and moon phases balance of forces are the largest influencer of marine habitats and their organisms’ adaptations imposing nature’s cyclical changes by tidal influence, and the most sensitive organisms are capable of registering these rather small-scale yet long-term alterations. The Sun, which is the “star of the show” at the center of our Solar System provides light and heat keeping everything on Earth alive, and it leads to the four seasons of Spring, Summer, Autumn, and Winter, which influence changes in temperature and amount of light on Earth. Environmental indicator organisms sense these changes.

The water above LBF has to permit enough light penetration through the water column for the success of their symbionts, and for reef symbionts, and also optimum abiotic parameters for every specific species in intertidal sites under variations of tidal oscillations. Other Forams from mangroves, estuaries and bays are controlled by a series of oscillating parameters (salinity, temperature, dissolved O₂, organic carbon) which often have no direct relationship with actual water depth, yet also serve as precise indicators of sea levels.

Zonation of calcareous and agglutinated foraminifera species depend on the amount of environment freshwater controlled by tide influence. Bay or lagoon environments with marine influence have calcareous forms; agglutinated forms represent brackish lagoons, marshes, and mangroves with less marine influence and higher freshwater influence, and LBF with symbiotic algae in the oceanic realm of reef areas.

Periods of high-frequency sea-level oscillations on the shoreline are confirmed by bottom calcareous bio facies followed by agglutinated ones, being precisely seasonally evidenced. The high-resolution response of microfauna to water level reconstructions based on freshwater and saline balance offers the potential to obtain more detailed and reliable records of relative sea-level change from salt marsh and mangrove sediments.

Sedimentation sites where emergence and submergence have taken place are combined with data to obtain a relatively complete sea-level history by understanding the dynamic of the community of Forams established which permits forecasting future impacts, with only a few as direct “Sea level Forecast” indicators, and have an interesting response in the present, with their ability to foresee future changes, allowing us to recommend actions to prevent losses.

Sea-level rise will directly affect mangroves and beaches where, for example, diverse fauna, which provides turtle nesting, will also be highly impacted by an encroaching ocean. Turtle and seabird nesting beaches are particularly vulnerable to rising sea levels, which will exacerbate beach erosion and flood nests. It is only possible to recommend strategies to protect natural as well as private and public resources with an acute understanding of the environment. With encroaching oceans, mangroves can advance towards land if they are backed by low-lying salt flats as sea levels rise. This can be an adaptation strategy to conserve the vegetation even though the tendency is to lose these important biomes with the existing anthropogenic pressure of its use from public and private infrastructure.

This chapter describes study cases in the south of Brazil in a mangrove area in São Paulo state, then in the reef areas of northeast Brazil, and we finish the chapter with samples collected from Deep Ocean in the north of Australia by the International Ocean Discovery Program (IODP), during Expedition 363, in the West Pacific Warm Pool (WPWP).

With limitations in terms of light, salinity and temperature, the response accuracy of bio indicators is fantastic, and one thing we can be sure of is that with sea-level rising in inundating and eroding coastal habitats, mangrove and reefs may be able to adapt, but only if sea-level rise occurs slowly, and if sufficient sediment exists to continue to accrete vertically to compensate for sea-level rise. These should be of paramount interest in paleoclimate studies, detecting oceanic to freshwater patterns, and reconstructing and forecasting sea levels from fossils and marine cores.

Benthic Forams species for in-situ organic matter flux are a water mass tracer in the northwestern tropical Pacific Ocean, indicating that distribution of lower bathyal and upper abyssal species are separated into two distinct groups. One that reflects relatively warm (>3.5 °C) intermediate depth water, with higher carbon flux (>3.5 g C m⁻² year⁻¹) versus a group that reflects colder, deeper waters with lower carbon flux. This data shows significant correlation with carbon flux and modern bottom water temperatures, reflecting lateral input of organic matter such as associated with down-slope movement. We have evidence for the use of the ‘warm’ water index as a tracer for water masses, at least in regions where the vertical flux of organic carbon is low and remains low throughout time.