Abhijit Mitra

Sea level rise (SLR) is not uniform globally; rather, it exhibits significant spatial variations, meaning that the same rise in sea level can have different effects in different regions of the world. These spatial variations result from a combination of natural and anthropogenic factors that influence the dynamics of sea level rise. The following are the main reasons why spatial differences occur in sea level rise:

1. Thermal Expansion and Local Climatic Conditions

Sea level rise due to thermal expansion of water depends on ocean temperature. In areas with higher ocean temperature increases (e.g., tropical and subtropical regions), water expands more than in colder ocean regions. However, this effect can vary locally due to ocean circulation patterns and other climatic factors influencing water temperatures. Different rates of ocean warming can cause uneven sea level rise in certain regions.

2. Gravitational and Ice Sheet Mass Effects

Massive ice sheets in polar regions (such as Greenland and Antarctica) influence global water flows and gravitational effects, which can lead to uneven sea level rise. As glaciers and ice caps in these regions melt, localized effects on sea level can be observed. In some areas where ice is melting, sea level rise may be higher, while in other places, farther from these processes, it may be lower.

3. Tectonic Processes and Land Movements

Geological movements, such as tectonic processes (e.g., land uplift or subsidence), can alter the elevation of the land and locally influence sea level rise. In areas prone to subsidence (such as river deltas or low-lying coastal regions), the effects of sea level rise may be more pronounced. Conversely, in regions with significant geological activity, such as continental margins or areas undergoing uplift (e.g., mountainous regions), sea level rise may be less noticeable.

4. Regional Ocean Current Cycles

Ocean currents play a critical role in the transfer of heat and water. In regions where currents increase the temperature of the water and concentrate heat, such as in equatorial and subtropical areas, thermal expansion will be higher, leading to more pronounced sea level rise. In contrast, in regions where ocean currents cool the ocean surface, the thermal expansion effect may be lower.

5. Changes in Regional Atmospheric Conditions

Changes in atmospheric pressure, such as cyclonic activity or long-term climatic conditions, can also influence sea level height. For instance, in areas prone to frequent and intense storms (such as hurricanes or cyclonic regions), there can be periodic increases in sea level height (known as "storm surge"), which is not directly related to long-term sea level rise but contributes to short-term spatial variations.

6. Local Human Activity

Human activities also contribute to spatial variations in sea level rise. For example, excessive groundwater extraction or the construction of large water barriers and levees can alter hydrological and marine processes. In some cases, areas with rapid urbanization or significant land subsidence may experience accelerated sea level rise.

Sea level rise shows spatial variations because it is influenced by various natural and anthropogenic factors. Each region has its specific geographic, climatic, and human factors that affect how sea level changes. Understanding these local variations is crucial for developing precise and effective adaptation strategies and managing the risks associated with sea level rise.

Sea level rise has become a standard indicator of how humans are transforming the planet. But our ideas about sea level, why we measure it, and how it varies have changed radically over the centuries...

"Over the last two centuries of the Holocene, human ideas about sea level and how it varies have changed drastically. In the eighteenth century, in continuity with older scholarly debates about the biblical flood, sea level was generally considered subject to continual decline. The earth, its mountains, and coasts were shaped primarily, many scholars affirmed, by the falling, over millennia, of a proto-ocean. From the turn of the nineteenth century, the stability of the sea and its use as the standard reference point for elevations became embedded into the Western scientific canon. And finally, in the last decades, the reality of a rising sea due to the impact of human activities on the geological scale has gained wide scientific acceptance.

To understand humanity’s future challenges in an environment that is less and less comparable to the one that nurtured our species over millennia, we must read the history of both oceanic sciences and surveying in a way that clarifies their relationship with the environments they claim to study. New ways of understanding these relationships may be the necessary outcome of unprecedented environmental changes in the Anthropocene."

https://issues.org/sea-level-history-hardenberg/

Sea level is affected by the melting of glaciers, changes in water density, changes in the bottom relief as a result of the dissolution of carbonates (-) and the removal of sand by rivers (+) and in the case of regional changes in gravity (the regional geoid of the Earth).

Three years ago I also started a discussion on this topic.

"Why can the level of the ocean tend to change in local areas of the sea or ocean? Why doesn't water level out due to gravity?"

As an example, I propose to consider the trend of increasing the level of the Black Sea as a whole and the trend of the formation of level rise anomalies in two local zones in the north and anomalies in the east (attached slide). We all understand that water from the Sea of ​​Azov can flow without obstacles into the Black Sea, and from the Black Sea into the Sea of ​​Marmara. I have attached a slide showing data on sea level changes in the Bosphorus. Usually the level in the Black Sea is only 3 centimeters higher than the Sea of ​​Marmara. The level of the Black Sea in 2005 was lower than in the Sea of ​​Marmara.

At the quantitative level, confirmation of the coincidence of the changes in Δǥ with the dynamics of the Earth's liquid shell in the area of ​​the Indian Ocean gravity anomaly was obtained (see Fig. 1 Map-scheme of the Earth's gravity field https://www.behance.net/gallery/2290102/ixtract-Most-Accurate-Gravity-Map-Of-The-Earth?locale=ru_RU

Based on satellite data on changes in the Earth's gravity field over time (the international GRACE project) and ocean surface topography (the international AVISO project), quantitative estimates were obtained of the presence, at a statistically significant level, of the conditionality of the anomalies of the ocean surface topography in the Arabian Sea to temporal changes in the gravity field.

First, the presence of a directly proportional relationship between changes in gravity and ocean level in the Arabian Sea area was established.

Second, it was determined that the gravity field and the shape of the geoid change in time exclusively with annual cycles.

Thirdly, it was established that the so-called "seasonal" changes in gravity and ocean level are coherent, but have a slight shift in physics.

Thus, at the quantitative level, it was confirmed for the first time that in the area of ​​the Indian Ocean gravity anomaly with a monsoon-type climate, the liquid (mobile) shell of the Earth fluctuates synchronously and with changes in Δǥ.

It is well known that rapid changes in the acceleration of free fall generate movements of atmospheric air. changes in gravity with an annual period generate vertical movements of the ocean and atmosphere. in the Indian Ocean region, vertical movements of the atmosphere are a component of the monsoon circulation of the atmosphere. (see Figure 2 Divergence and convergence over India at the level of 200 hPa a) in August, b) in February 27. http://www.cpc.noaa.gov)).