Where is phytoplankton most productive

The decrease reflects the inability of photoacclimation to maintain sufficient light absorption at all light levels. Discrete measurements of NPP determined using 24 h 14 C-uptake see below were used to ground-truth modeled productivity values.

NPP was determined using 14 C uptake incubations. Water collected pre-dawn from 4 to 5 depths was inoculated with 14 C-labeled sodium bicarbonate and incubated in on-deck incubators at light levels corresponding to the collection depths. Following incubation 24 h, dawn-to-dawn , samples were filtered onto 0. Filters were flash-frozen and stored in liquid nitrogen until analysis. All pigments were normalized to total Chl a concentration before a network-based community detection analysis was performed following the methods of Kramer et al.

Briefly, in the network-based community detection analysis, each sample becomes a node in the network; the edges connecting each sample to all other samples are described by the strength of the correlation between the sites. Based on similarities in physical-chemical properties and highly-defined phytoplankton community composition, we grouped subarctic and temperate provinces together and subtropical and Sargasso Sea provinces together following the approach of Bolanos et al.

These broader groups are hereafter referred to as the subarctic and subtropical regions, respectively. Water column stratification and upper ocean mixing dynamics showed strong seasonality across the four campaigns. Figure 3. Blue line indicates interpolated values between casts over the course of the science intensive transect, black circles indicate MLD values estimated from CTD profiles. E—H Median mixed layer light levels I g , moles of photons m —2 h —1.

Orange circles are HPLC-based estimates of surface chlorophyll concentration. Table 2. Mean and standard deviation, maximum and minimum values of physical, biological and chemical parameters measured during the four NAAMES field campaigns.

Annual cycles of mixing, stratification, and light availability Figures 3A—H yielded minimum C phyto and Chl concentrations in winter, an accumulation of phytoplankton biomass in spring reaching a late spring climax, followed by an autumn decline in both properties in the subarctic and subtropical regions Figures 3I—L.

One difference between the two regions is that the subarctic climax biomass appeared slightly elevated compared to subtropical levels Figure 3K. Figure 4. Figure 5. Points show daily mean with error bars indicating standard deviations.

Symbol shape indicates the dominant phytoplankton within the community, estimated using a community detection algorithm. Previously published relationships are also shown from Behrenfeld et al. Potential reasons for the apparent offset are discussed below. Figure 6. Net primary production NPP estimated using carbon uptake 14 C incubations compared with modeled estimates. Symbol shape indicates the dominant phytoplankton taxa within the community, estimated using a community detection algorithm.

Figure 7. Black solid line indicates depth-resolved 1 m model estimates of NPP. Gray circles are discrete estimates of carbon-uptake measured in 24 h 14 C bottle incubations. Dashed black line shows the depth of the mixed layer. Dashed gray line shows the depth of the euphotic zone.

White boxes indicate the station was in the subtropical region, gray shading indicates stations in the subarctic. Each row is a different phase of the annual cycle labeled on right. Thus, during winter, growth rate was the primary driver of NPP in the subtropical region, whereas the standing stock of phytoplankton carbon drove NPP in the subarctic region.

Table 3. Figure 8. Each point represents a daily estimate of data collected while on station. Boxes represent the median, first and third quartiles, whiskers are 1. The ability to explain what drives spatio-temporal variability in phytoplankton productivity is essential for improving our understanding of global carbon dynamics. Early satellite-based approaches used Chl and predictive relationships with abiotic factors e.

More recently, phytoplankton growth was estimated using changes in Chl and C phyto as a function of light, temperature, and nutrients Behrenfeld et al.

Despite a difference of almost 30 years between the two studies, the observations show very similar values. Unique to this analysis of the NAAMES campaigns is the ship-based optical assessment of phytoplankton growth rate, which can help discern the abiotic and biological controls on the annual bloom cycle.

Phytoplankton growth, and consequently NPP, is a function of light, temperature and nutrients Geider et al. While light harvesting is subject to a variety of strategies that ultimately dictate the maximal rate of division, the scarce availability of nutrients also requires physiological adjustments that involve highly efficient tuning of downstream carbon metabolism MacIntyre et al.

Phytoplankton strategies to optimize growth in response to light and nutrient availability appear to be shared by a diverse array of species, with distinct physiologies and evolutionary pathways Halsey et al.

The contrasting regimes of light and nutrient availability identified in the different regions in NAAMES resulted in distinct growth dynamics over the annual cycle. These behaviors have important implications for phytoplankton taxonomic succession, trophic energy transfer, and carbon export efficiency the fraction of NPP exported out of the euphotic zone.

The faster division rate measured in the subtropical region is unsurprising as the growth conditions encountered here during the four field campaigns were highly favorable: higher growth irradiance I g , greater physical stability of the water column, and moderate nutrient availability except for the equilibrium phase; Supplementary Figures S2 , S3.

In contrast, I g in the subarctic winter transition was an order of magnitude lower 0. This appeared to result in severe light limitation, which inhibited growth in the surface layer and concurs with previous findings from this region Follows and Dutkiewicz, ; Henson et al. The subtropical region defined in this study falls into a transition zone described by Henson et al. The conditions giving rise to this acceleration were also evident in the subarctic region, and the maximal mean growth rates observed across the two regions were similar Figure 8.

Nutrient availability mainly N only approached limiting concentrations in the subtropical region during the equilibrium phase Figure 9. Figure 9. The shape of each point indicates the dominant phytoplankton taxa estimated using a pigment-based community detection analysis.

Dashed line indicates the Redfield ratio of N:P The stability of an ecosystem can strongly influence the diversity and survival strategy of the resident population Tilman, Within the marine environment, stability is quite often a reference to physical properties, such as the strength of stratification which is inversely correlated to the rate of vertical mixing.

Seasonal variability in stratification or stabilization of the water column is a key feature of many prominent phytoplankton bloom hypotheses Sverdrup, ; Huisman et al. In the western North Atlantic, it could be argued that the two regions subtropical and subarctic offer contrasting regimes of ecosystem stability, which have a profound influence on the taxonomy, growth and productivity of the phytoplankton community, and in turn, carbon export.

The growth dynamics discussed in the previous section provide insight into factors that shape the annual cycle of phytoplankton biomass, particularly the magnitude and termination of a bloom. During this time, a more substantial 4-fold change in biomass was observed as phytoplankton growth exceeded losses, leading to accumulation. The extent of accumulation, however, was significantly lower than the 7-fold change in biomass observed in the sub-arctic over the same period, during which the acceleration of growth in this region was much faster.

The differences between the two regions could be explained by a tight coupling of growth-loss processes in the subtropics, with significant accumulation quickly curtailed by recoupling of grazer control amongst other loss processes following a mild acceleration in phytoplankton growth.

Such tight coupling was likely driven by the generally stable growth conditions high light, shallow mixed layer in the subtropical region that facilitated consistently high phytoplankton growth rates, which in turn provided a permanent food source for higher trophic levels Banse, In contrast, stronger decoupling from these loss processes likely occurred in the subarctic during the winter, when deeper vertical mixing resulted in more extreme light-limited growth conditions.

Under such conditions, dilution of phytoplankton standing stocks would have reduced predator—prey encounter rates, resulting in a decline in predator abundance Behrenfeld, ; Mayot et al.

Collectively, these observations support the tenet of the Disturbance-Recoupling Hypothesis of bloom control, namely that the balance of phytoplankton growth and loss by predation determines bloom initiation and termination Behrenfeld and Boss, The similar concentrations of biomass observed in the two regions during the winter transition is most likely explained by fewer, larger cells in the subarctic.

Such divergent environments can result in very different strategies of survival and growth by the phytoplankton population, which can in turn influence the life cycles of key grazers that ultimately shape the development of a bloom Friedland et al. As the winds reverse direction offshore versus onshore , they alternately enhance or suppress upwelling, which changes nutrient concentrations.

In the equatorial upwelling zone, there is very little seasonal change in phytoplankton productivity. In spring and summer, phytoplankton bloom at high latitudes and decline in subtropical latitudes.

These maps show average chlorophyll concentration in May — left and November — right in the Pacific Ocean. ENSO cycles are significant changes from typical sea surface temperatures, wind patterns, and rainfall in the Pacific Ocean along the equator. Compared to the ENSO-related changes in the productivity in the tropical Pacific, year-to-year differences in productivity in mid- and high latitudes are small.

Life Water. This high efficiency of decomposition is due to the fact that the organisms carrying out the decomposition rely upon it as their sole source of chemical energy; in most of the open ocean, the heterotrophs only leave behind the organic matter that is too chemically resistant for it to be worth the investment to decompose. Productivity in coastal ecosystems is often distinct from that of the open ocean. Along the coasts, the seafloor is shallow, and sunlight can sometimes penetrate all the way through the water column to the bottom, thus enabling bottom-dwelling " benthic " organisms to photosynthesize.

Furthermore, sinking organic matter isintercepted by the seabed, where it supports thriving benthic faunal communities, in the process being recycled back to dissolved nutrients that are then immediately available for primary production.

The proximity to land and its nutrient sources, the interception of sinking organic matter by the shallow seafloor, and the propensity for coastal upwelling all result in highly productive ecosystems.

Here, we mainly address the productivity of the vast open ocean; nevertheless, many of the same concepts, albeit in modified form, apply to coastal systems.

Phytoplankton require a suite of chemicals, and those with the potential to be scarce in surface waters are typically identified as "nutrients. Dissolved inorganic carbon , which is the feedstock for organic carbon production by photosynthesis , is also abundant and so is not typically listed among the nutrients.

However, its acidic form dissolved CO 2 is often at adequately low concentrations to affect the growth of at least some phytoplankton. Broadly important nutrients include nitrogen N , phosphorus P , iron Fe , and silicon Si. There appear to be relatively uniform requirements for N and P among phytoplankton. As Redfield noted, the dissolved N:P in the deep ocean is close to the ratio of plankton biomass, and we will argue below that plankton impose this ratio on the deep, not vice versa.

Research is ongoing to understand the role of other trace elements in productivity Morel et al. Silicon is a nutrient only for specific plankton taxa-diatoms autotrophic phytoplankton , silicoflaggellates, and radiolaria heterotrophic zooplankton — which use it to make opal hard parts. However, the typical dominance of diatoms in Si-bearing waters, and the tendency of diatom-associated organic matter to sink out of the surface ocean, make Si availability a major factor in the broader ecology and biogeochemistry of surface waters.

Sunlight is the ultimate energy source — directly or indirectly — for almost all life on Earth, including in the deep ocean. Thus, photosynthesis is largely restricted to the upper light-penetrated skin of the ocean. Moreover, across most of the ocean's area, including the tropics, subtropics, and the temperate zone, the absorption of sunlight causes surface water to be much warmer than the underlying deep ocean, the latter being filled with water that sank from the surface in the high latitudes.

Warm water is more buoyant than cold, which causes the upper sunlit layer to float on the denser deep ocean, with the transition between the two known as the "pycnocline" for "density gradient" or "thermocline" the vertical temperature gradient that drives density stratification across most of the ocean, Figure 2. Wind or another source of energy is required to drive mixing across the pycnocline, and so the transport of water with its dissolved chemicals between the sunlit surface and the dark interior is sluggish.

This dual effect of light on photosynthesis and seawater buoyancy is critical for the success of ocean phytoplankton. If the ocean did not have a thin buoyant surface layer, mixing would carry algae out of the light and thus away from their energy source for most of the time. Instead of nearly neutrally buoyant single celled algae, larger, positively buoyant photosynthetic organisms e. This hypothetical case aside, although viable phytoplankton cells are found albeit at low concentrations in deeper waters, photosynthesis limits active phytoplankton growth to the upper skin of the ocean, while upper ocean density stratification prevents them from being mixed down into the dark abyss.

Figure 2 Typical conditions in the subtropical ocean, as indicated by data collected at the Bermuda Atlantic Time-series Station in July, The thermocline vertical temperature gradient stratifies the upper water column.

During this particular station occupation, the shallow wind-mixed surface layer is not well defined, presumably because of strong insolation and a lack of wind that allowed continuous stratification all the way to the surface. New supply of the major nutrients N and P is limited by the slow mixing across the upper thermocline showing here only the N nutrient nitrate, NO 3 -.

Within the upper euphotic zone, the slow nutrient supply is completely consumed by phytoplankton in their growth. This growth leads to the accumulation of particulate organic carbon in the surface ocean, some of which is respired by bacteria, zooplankton, and other heterotrophs, and some of which is exported as sinking material.

The deep chlorophyll maximum DCM occurs at the contact where there is adequate light for photosynthesis and yet significant nutrient supply from below. The DCM should not be strictly interpreted as a depth maximum in phytoplankton biomass, as the phytoplankton at the DCM have a particularly high internal chlorophyll concentration. At the same time, the existence of a thin buoyant surface layer conspires with other processes to impose nutrient limitation on ocean productivity. The export of organic matter to depth depletes the surface ocean of nutrients, causing the nutrients to accumulate in deep waters where there is no light available for photosynthesis Figure 2.

Because of the density difference between surface water and the deep sea across most of the ocean, ocean circulation can only very slowly reintroduce dissolved nutrients to the euphotic zone. By driving nutrients out of the sunlit, buoyant surface waters, ocean productivity effectively limits itself. Phytoplankton growth limitation has traditionally been interpreted in the context of Liebig's Law of the Minimum, which states that plant growth will be as great as allowed by the least available resource, the "limiting nutrient" that sets the productivity of the system de Baar While this view is powerful, interactions among nutrients and between nutrients and light can also control productivity.

A simple but important example of this potential for "co-limitation" comes from polar regions, where oblique solar insolation combines with deep mixing of surface waters to yield low light availability. In such environments, higher iron supply can increase the efficiency with which phytoplankton capture light energy Maldonado et al. More broadly, it has been argued that phytoplankton should generally seek a state of co-limitation by all the chemicals they require, including the many trace metal nutrients Morel In contrast to the terrestrial biosphere, most marine photosynthesis is conducted by single-celled organisms, and the more abundant of the multicellular forms are structurally much simpler than the vascular plants on land.

This size range is composed mostly of eukaryotes, organisms whose cells contain complex membrane-bound structures "organelles" , including the cell's nucleus and chloroplasts. Well-studied forms of eukaryotic phytoplankton include the opal-secreting diatoms, prymnesiophytes including the CaCO 3 -secreting coccolithophorids , and the organic wall-forming dinoflagellates. The centrality of these organisms in early oceanographic thought was due to their accessibility by standard light microscopy.

Only with recent technological advances have smaller organisms become readily observable, revolutionizing our view of the plankton. In , he discovered the RMS Titanic , and has succeeded in tracking down numerous other significant shipwrecks, including the German battleship Bismarck , the lost fleet of Guadalcanal, the U.

He is known for his research on the ecology and evolution of fauna in deep-ocean hydrothermal, seamount, canyon and deep trench systems. He has conducted more than 60 scientific expeditions in the Arctic, Atlantic, Pacific, and Indian Oceans. Sunita L. Her research explores how the larvae of seafloor invertebrates such as anemones and sea stars disperse to isolated, island-like habitats, how larvae settle and colonize new sites, and how their communities change over time.

Kirstin also has ongoing projects in the Arctic and on coral reefs in Palau. Her work frequently takes her underwater using remotely operated vehicles and SCUBA and carries her to the far corners of the world. What are Phytoplankton? Why are they important? August 20, Specialized camera system gives unprecedented view of ocean life With still so much to learn about the planktonic creatures that support the marine food web, scientists with the Northeast U.

November 16, Long-running plankton study to resume off of Maine. August 21, The Recipe for a Harmful Algal Bloom Harmful algal blooms can produce toxins that accumulate in shellfish and cause health problems and economic losses. August 14, Life at the Edge What makes the shelf break front such a productive and diverse part of the Northwest Atlantic Ocean? April 17, Mission to the Ocean Twilight Zone The twilight zone is a part of the ocean to 3, feet below the surface, where little sunlight can reach.

Minion robots in the Ocean Twilight Zone. Forecasting Where Ocean Life Thrives. Setting a Watchman for Harmful Algal Blooms. Imaging FlowCytobot Real-time observation of phytoplankton. Video Plankton Recorder An underwater video microscope system that that takes images of plankton and particulate matter. Related Topics Coral. Emperor Penguins. Marine Mammals. Microbial Life. Ocean Twilight Zone. Right Whales.