4.1. Dissolved minerals in the water
Phytoplankton also needs inorganic nutrients such as nitrate, silicate, phosphate, and iron, turning them into proteins, fats, and carbohydrates. Figure 2 shows that the Indian Ocean, dissolve Iron rapid increase (0.1–0.2 mmol/m³/yr) in the last decade may lead to the electron carrier chain of photosynthesis of phytoplankton, but the past decade’s increasing rate was downgraded (0.05–0.08 mmol/m³/yr). In the Southern Ocean with high surface concentrations of the major nutrients (Nitrate, Phosphate, silicate), iron addition experiments on distinct scales have consistently yielded extensive enrichment of NPP, increases in biomass, and changes in phytoplankton assemblage. In this first decade light incising trend but last decade, again it is going into a negative trend. The Arctic and North Atlantic oceans have intense negative tendencies that may limit the NPP of the regions. Timor, Arafura, coral, and the South China Sea have a very high magnitude negative trend. Still, in the last decade, it switched because of the Australian drought due to the Indian Ocean Dipole (IOD) effects and the strengthening of summer ITCZ and subtropical highs. The Asian-Australian monsoon fluctuations from year to year are the El Nino Southern Oscillation (ENSO), El Nino warming, and La Nina cooling in the equatorial Pacific dominate nutrients dynamic and productivity in the region. The number of hypotheses regarding past ocean productivity centered on Nitrate migrations and the budget of dissolve nitrate is largely biologically driven. In our study, we have seen the first-decade central pacific ocean, Scotia sea, and southern front of the Indian ocean have a positive trend (0.5-1.0 mmol/m³/yr) and Bering, Chukchi, Beaufort Sea have a high positive trend (1.5-2.0 mmol/m³/yr). However, Amundsen, Barents, Norwegian, Greenland, Laptev, and East Siberian Sea have a modestly negative trend (~ 0.7-1.0 mmol/m³/yr). In the last decade central Pacific Ocean, Bering, and the Chukchi Sea switched over to a deep negative trend, and the Amundsen Sea exhilarated to a deep negative trend due to Southern oscillation and warming. So Phytoplankton increase had principally supported by recycling nutrients or reintroducing nutrients from the bottomless ocean by mixing. Though external or new nutrients have fueled a tiny portion of primary production, it has the nutrients that limit the amount of carbon that had sequestered long-term in the deep ocean. The coupling between N and P in the sea may be weakened by variation in the N: P stoichiometry of plankton and productivity. Silicate is most important for the diatom's life cycle, a phytoplankton group that has pervasive throughout the global ocean and is often dominant in temperate to Southern and Arctic Oceans. Dissolved Silica is most likely crucial for variations in the characteristics and spatial variation of ocean productivity. We found that Amundsen, Beaufort, and Gulf of Alaska very steady downgrading trend rate of ~ 1.0 to ~ 2.0 mmol/m³/yr, but the central Atlantic, Pacific, and spatially the Caribbean Sea emerging negative trend has responsible for Nano plankton and diatom growth of the region. Silicate availability is much lower in tropical and subtropical oceans than in polar and temperate waters. However, diatoms are still present in these regions, meaning the pervasive occurrence of diatoms even in the low latitudes has at least partly been due to lower silicate requirements in low-latitude species. Nevertheless, the vigorous recycling process of silica within tropical warming in low latitude surface waters, where biogenic opal is higher soluble. The long-term dynamics of the dissolved silicate reservoir and its impacts are too uncertain. Preferably, we focus on the dynamics of this nutrient in the modern ocean, which gives some insight into its potential changes over time. Upper-ocean silicate recycling diatoms contribute more to the sinking flux of organic matter than they do to NPP.
4.1. Minerals dust deposition on the ocean surface
Aerosols supply bio-accessible nutrients to marine biota, which would assist NPP. Aerosol deposition (wet and dry) is a vital reservoir of macro and micronutrients (N, P, C, Si, and Fe) supplied to oceans2. However, Metal dissolution from aerosol concentration to the ocean's water is crucial in intensifying and restraining phytoplankton growth rates and changing the plankton community. Mineral dust dosing rate into the atmosphere can alter dust storms, volcanic eruptions, and anthropogenic actions. Rapid urbanization, drought, enhanced desertification, and land-use change have profoundly affected the amount of mineral dust concentrated in ocean water. Figure 3 shows that the 1998–2008 period saw a steady increase of 10–15% in Aerosol components over ocean, but the north Indian Ocean, China Sea, and the Gulf of Guinea have a high degree of positive trend because desert and semi-desert are dust (particulates matter) loading. The last decade has had a high-level reduction (20–30%). We found deep negative trends in aerosol particles, and the Arabian Sea, Bay of Bengal, Guinea Sea, and Caribbean Sea have likely positive trends. The South Indian Ocean, Weddell Sea, and Arafura Sea have a very reasonable positive trend. Organic and Black carbon shows a 5–8% rise in the last two decades, but the Okhotsk and Japan seas have a negative trend. The North Indian Ocean, Japan, and the South China Sea encountered a high AOD reduction (20–30%). Eastern Sahara dust spray toward the NAO first decade shows a shallow reduction in it but last decade, it switched over. The Organic carbon (OC) deposition in the North Pacific Ocean in the last decade shows a 10–20% reduction, which is more alarming for this region NPP. Organic carbon contains multiple micronutrients that are very important for the phytoplankton life sustain of this HNLC region. The Alaskan Gyre (AG) and the Western Subarctic Gyre (WSG) phytoplankton, pteropods, and Mesozooplankton population are under threat due to the lessened OC deposition of the region.
4.3. Physical factors
We fundamentally determined that phytoplankton is expected to grow more gradually in warmer ocean conditions; its turn will lessen the food available for fish and other marine organisms, thus seriously affecting the ocean's food chain. Decreasing phytoplankton growth rates and productivity would intend that more limited CO2 taken by the sea, which could hasten global warming and contribute to a vicious cycle of enhanced warming. The Anthropogenic potential to turn a warmer climate would inevitably alter atmosphere-ocean CO2 exchange patterns, ecosystem, and marine food networks. In recent decades Ocean surface density has changed due to warming, mesoscale salinity, and circulation change limiting regional productivity, and biodiversity, and increasing toxic algal bloom. Figure 4 shows that the first-decade regional density change was very stable, but last decade Central Indian Ocean had a severe negative trend rate of -0.08 to -0.12 kg/m³/yr; Central Pacific, Gulf of Alaska have ~ 0.15 to ~ 0.18 kg/m³/year. In addition, the Mid-Atlantic region and Bermuda have − 0.10 to -0.12 kg/m³/yr. El Nino and La Nino are the ocean-atmosphere coupling autocratic tone of variability in the Earth-climate system with a typical recurrence of 2–7 years in the Pacific. The robust indication that throughout Eastern Pacific (EP) and Central Pacific (CP) types of El Nino, influences upon primary productivity can be observed throughout, tend to be most significant in the tropics and subtropics, including up to 40% of the total affected regions. We introduce that analysis of the principal tools forcing the biophysical under thermal and density variability may contribute a helpful guide to improve our understanding of changes in the marine ecosystem in a warming climate situation.
The Gulf of Alaskan and Peru-Chile sea ocean warming accelerated last decade at 0.15°C/yr than the first decade, spatially eastern Aleutian trench region. The central Pacific is also warming significantly faster than in the previous decade. The first decade of the Arctic cold blob shows a positive trend (0.05–0.1°C/yr), but in the last decade, it is emerging; the negative trend is ~ 0.1 to ~ 0.2°C/yr. The Central North Atlantic and Sargasso Sea's first decade had a negative trend (-0.03 to -0.07°C/yr), but in the last decade, it switched to warming (0.08–0.12°C/yr). The Equatorial Atlantic in the first decade had shallow warming but the last decade showed a marginal rate of warming (~ 0.02 to ~ 0.03°C/yr), and the Gulf of Guinea last decade had moderate warming (0.04–0.05°C/yr). The Indian Ocean showed an increasing trend in the last decade (0.03–0.05°C/yr). The Bay of Bengal and the equatorial Arabian Sea have a very shallow negative trend but Last decade switched to a positive trend (0.02–0.04°C/yr); especially Sri Lanka Dome (SLD) region, Gulf of Persian and, Gulf of Oman warming evident (0.08–0.10°C/yr). Positive Indian Ocean Dipole effects are also visible in the Western Australian coastal region (negative trend; ~0.08 to ~ 0.12°C/yr), but this negative trend was shrinking toward the open ocean in the last decade.
4.4. Nutrients transport and mixing
This analysis reveals that mesoscale ocean currents and eddies take a massive role in nutrient transportation; for instance, the Southern Ocean has evolved into a cold, profoundly productive region because of the hydrodynamic nature of the region. World central upwelling regions like Indian Ocean Somalia current forced gulf of Arabian Sea, Benguela currents forced gulf of Guinea, canary currents forced Gambia coast, Peru currents forced Peru coast. Californian currents forced San Francisco, and Mexico coast upwelling zones to be more productive than others do; Deepwater is upwelled toward the Polar Ocean surface water. The winds pumped this nutrient-bearing water into the middle-depth to the bottomless ocean, contributing nutrients to the low latitude surface ocean. The central upwelling systems in the Indian Ocean have the western Arabian Sea (WAS), Sri Lanka Dome (SLD), Sumatra coasts (SC), Seychelles-Chagos Thermocline Ridge (SCTR), take a crucial role in nutrient dynamics as well primary productivity. The southwest tropical Indian Ocean (SWTIO) is a vital upwelling area in the Indian Ocean region due to the Seychelles-Chagos Thermocline Ridge (SCTR) system portrayed by a thermocline shallower than the euphotic zone. The SWTIO has been influenced by the seasonally changing monsoon wind systems that serve as the vital physical driver for the usual upwelling processes resulting in notable variability in sea surface temperature (SST), increased surface stratification restraining vertical mixing, thereby shortening the number of nutrients into the well-lit euphotic zone where photosynthesis takes place. This phytochemical control of the chlorophyll-a distribution during winter and summer monsoons opined that surface freshening guides the chlorophyll-a by modulating latent stability and mixed layer depth. These existing oligotrophic situations in the southwest tropical Indian Ocean (SWTIO) have delivered economic phytoplankton productivity (PP) recorded in this region. Tropical Ocean warming and acidification reduce net primary productivity (NPP) across the largest of the tropics because of surface thermal stratification; their results imply a decrease in NPP concerning the growing sea surface temperature across the western Indian Ocean. Our study infers that ocean upwelling transports nutrient-rich water and microbial species and controls SST and Spco2 solubility. Figure 5 shows that in the first decade arctic ocean shows a positive trend (0.010–0.012 Pa/yr) but last decade it changed to a shallow negative trend (~ 0.014–0.016 Pa/yr); except clod blob region, there are very high positive trend shows (0.018–0.020 Pa/yr) that’s why there mixed layer depth also increased. In this following region last decade, MLD shows a very high positive trend of 15–20 m/yr. In the southern ocean's first decade, WS shows a very high negative trend (~ 0.014–0.016 Pa/yr) but last decade, it switched to a very high positive trend (0.016–0.020 Pa/yr). In addition, overall Pacific Ocean shows in the first decade shallow positive trend but last decade it again shows a negative trend; especially the central pacific and Indian Ocean shows a similar pattern. The gulf of Alaskan shows a very high negative trend (0.016–0.020 Pa/yr) in both decades. Surface currents velocity (SCV) and eddy kinetic energy (EKE) show similar features in both decades. In the first decade it was a shallow negative trend but last decade, a speedup has shown, especially in the tropical ocean. We also observe that in the first decade, global ocean mixed layer depth increased (10–20 m/yr) but in the last decade, the Pacific Ocean showed a very high negative trend (~ 15–20 m/yr). However, the Indian Ocean and Atlantic Ocean MLD increasing rate shallows in the last decade by at least 5 m/yr.