Despite its cold waters and harsh winds, the North Sea is a fertile basin for phytoplankton blooms. The drifting, plantlike organisms tend to be most abundant in late spring and early summer due to high levels of nutrients in the water and increasing sunlight. The intense winds blowing over the relatively shallow North Sea causes a lot of vertical and horizontal mixing that brings nutrients to the surface, as does runoff from European rivers.
The first image, acquired on June 6, 2015, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, shows a mass of phytoplankton blooming between Denmark, the United Kingdom, and Germany. The milky, light-colored surface waters are likely filled with coccolithophores, whereas the greener areas are probably rich with diatoms or perhaps dinoflagellates. (It is impossible to know for sure without water samples.) Colors are more intense and vivid in places where concentrations of phytoplankton are highest, which should match where nutrients like nitrates, phosphates, iron, and sulfur are most abundant and water temperatures are ideal. The patterns traced by the phytoplankton also give some insight to the currents and eddies in the area.
On June 11, 2015, the MODIS instrument on NASA’s Aqua satellite caught a glimpse (middle image) of the same area in what was likely a different stage of the bloom cycle. Areas of concentrated phytoplankton are smaller, and most have the milky color characteristic of coccolithophores; there are few to no green areas. The change could be due to the short life span of phytoplankton—two to six days—and differences between the species. Some outlast others because of their ability to survive at lower nutrient levels.
The third image, taken on July 1, 2015, by MODIS on Terra, shows an area slightly north of the earlier bloom. It could be a new burst of coccolithophores, or it could be a continuation and migration of the same bloom from earlier in June.
Some researchers have found that numbers of plankton can actually begin to increase in the middle of winter, when growth conditions would seem to be at their worst. Studies suggest that winter storms churn the ocean and cause deep water mixing. This water mixing allows for phytoplankton to grow and live at depth without being spotted by their predators. When spring arrives, phytoplankton can fully bloom because not only are the nutrients available, but there is a longer period of sunlight.
NASA Earth Observatory images by Jesse Allen, using data from the Level 1 and Atmospheres Active Distribution System (LAADS). Caption by Rachel Carlowicz with Mike Carlowicz. Interpretation insight provided by Mike Behrenfeld, Oregon State University, and Jochen Wollschläger, Helmholtz-Zentrum Geesthacht.
Licha ya maji yake baridi na upepo mkali, Bahari ya Kaskazini ni bonde lenye rutuba kwa ajili ya maua ya mimea ya plankton. Mimea hiyo huishi mwishoni mwa majira ya kuchipua na mapema wakati wa kiangazi kwa sababu ya kiasi kikubwa cha virutubisho katika maji na kuongezeka kwa mwangaza wa jua. Upepo mkali unaovuma juu ya Bahari ya Kaskazini, ambayo ni ya chini sana, husababisha mchanganyiko mwingi wa wima na wa usawa ambao huleta virutubisho juu, kama vile maji kutoka mito ya Ulaya. Picha ya kwanza, iliyopigwa Juni 6, 2015 na Moderately Resolved Imaging Spectroscopy (MODIS) kwenye satelaiti ya NASA ya Terra, inaonyesha wingi wa phytoplankton inayositawi kati ya Denmark, Uingereza na Ujerumani. Maji ya juu yenye rangi nyangavu na yenye rangi nyangavu yaweza kuwa na viumbe aina ya coccolithophores, ilhali maeneo yenye rangi ya kijani-kibichi yaweza kuwa na viumbe aina ya diatoms au dinoflagellates. (Haiwezekani kujua kwa uhakika bila sampuli za maji.) Rangi ni kali zaidi na wazi katika maeneo ambapo viwango vya phytoplankton ni juu, ambayo inapaswa kufanana ambapo virutubisho kama nitrates, phosphates, chuma, na sulfuri ni wengi na joto la maji ni bora. Mifumo iliyochorwa na phytoplankton pia hutoa ufahamu fulani kuhusu mikondo na minyororo katika eneo hilo. Mnamo Juni 11, 2015, vyombo vya MODIS kwenye satelaiti ya NASA ya Aqua vilipata picha ya eneo hilo katika hatua tofauti ya mzunguko wa maua. Maeneo ya phytoplankton iliyojaa ni madogo, na mengi yana rangi ya maziwa ya coccolithophores; kuna maeneo machache ya kijani kibichi. Mabadiliko hayo yanaweza kusababishwa na muda mfupi wa maisha ya phytoplankton - siku mbili hadi sita - na tofauti kati ya spishi. Baadhi yao huishi muda mrefu kuliko wengine kwa sababu ya uwezo wao wa kuishi wakiwa na viwango vya chini vya virutubisho. Picha ya tatu, iliyochukuliwa Julai 1, 2015 na MODIS kwenye Terra, inaonyesha eneo la kaskazini kidogo ya maua ya mapema. Inaweza kuwa mlipuko mpya wa coccolithophores, au inaweza kuwa mwendelezo na uhamiaji wa maua sawa kutoka mapema Juni. Watafiti fulani wamegundua kwamba idadi ya plankton huanza kuongezeka katikati ya majira ya baridi kali, wakati hali za ukuzi zinaonekana kuwa mbaya zaidi. Uchunguzi unaonyesha kwamba dhoruba za majira ya baridi kali huchochea bahari na kusababisha mchanganyiko wa maji ya kina kirefu. Mchanganyiko huo wa maji huruhusu phytoplankton kukua na kuishi katika kina bila kuonekana na wawindaji wao. Wakati wa majira ya kuchipua, phytoplankton inaweza kuota kwa sababu sio tu virutubisho vinapatikana, lakini kuna kipindi kirefu cha mwanga wa jua. Picha za NASA Earth Observatory na Jesse Allen, kutumia data kutoka ngazi ya 1 na Atmospheres Active Distribution System (LAADS). Maandishi ya Rachel Carlowicz na Mike Carlowicz. Maelezo ya tafsiri yaliyotolewa na Mike Behrenfeld, Chuo Kikuu cha Jimbo la Oregon, na Jochen Wollschläger, Helmholtz-Zentrum Geesthacht.