{"id":477826,"date":"2026-10-09T07:28:14","date_gmt":"2026-10-09T14:28:14","guid":{"rendered":"https:\/\/climatescience.press\/?p=477826"},"modified":"2026-10-09T07:28:17","modified_gmt":"2026-10-09T14:28:17","slug":"tiny-baltic-sea-microbes-clump-together-to-ferry-carbon-into-the-deep","status":"publish","type":"post","link":"https:\/\/climatescience.press\/?p=477826","title":{"rendered":"Tiny Baltic Sea microbes clump together to ferry carbon into the deep"},"content":{"rendered":"\n
\"Underwater
AI generated by Grok<\/figcaption><\/figure>\n\n\n\n

Tiny photosynthetic organisms (picocyanobacteria, mainly Synechococcus<\/em> strains smaller than 2 micrometers) in the Baltic Sea can substantially help transport carbon from surface waters to deeper layers by forming colonies and aggregates that sink more readily.<\/strong><\/p>\n\n\n\n

A study from the Department of Ecology, Environment and Plant Sciences at Stockholm University<\/strong> (led by Martin Ekman, with co- author Rachel Foster) shows that the tendency of different strains to aggregate directly controls how much of their biomass<\/strong> is exported downward. <\/p>\n\n\n\n

Individual cells are too small to sink efficiently on their own, but colony- forming strains<\/strong> appear more often in larger size fractions and in sediment-trap material. Their contribution to exported biomass was broadly proportional to their abundance in surface waters (often a large share of the phytoplankton community).<\/p>\n\n\n\n

Researchers sampled surface water plus depths of 25 m and 75 m at Landsort Deep (a long- term monitoring site) during spring and summer, used sediment traps below the sunlit zone, and combined microscopy, flow cytometry, size fractionation (>10 \u00b5m vs. free\/small cells), and genetic sequencing (16S rRNA). <\/p>\n\n\n\n

Seasonal differences appeared between colony- forming and mostly single- cell strains, suggesting aggregation is an important ecological trait.<\/p>\n\n\n\n

This matters for the biological carbon pump:<\/strong> phytoplankton photosynthesis takes up CO\u2082, and sinking biomass moves that carbon deeper, helping regulate atmospheric CO\u2082. Remineralization of the sinking material also contributes to oxygen- poor (anoxic) bottom waters in places like the Baltic Sea. <\/p>\n\n\n\n

Because picophytoplankton are expected to become more abundant in warmer, more stratified, nutrient-poorer future oceans, understanding how their biomass can still be exported is relevant for predicting carbon cycling and atmospheric CO\u2082 levels. The authors note that similar processes should be checked in other picophytoplankton-dominated regions, such as open- ocean gyres.<\/p>\n\n\n\n

The peer- reviewed paper is \u201cDifferential aggregation properties among Baltic Sea picocyanobacterial strains impact their export,\u201d published in The ISME Journal<\/em> (2026).<\/p>\n\n\n\n

\"Microscopic
Micrograph of phytoplankton from Landsort Deep, BY31, the long-term monitoring site of the Baltic Sea where samples were taken for the reported study. In the upper left corner is a large diatom, Chaetoceros danicus, distinguished by its long spines protruding from the cell, a few large colonies and aggregates of picocyanobacteria lie in the background, and in the bottom middle are two pigmented and compacted colonies of the cyanobacteria Woronichinia next to two filaments of the N2-fixing cyanobacteria Aphanizomenon. Credit: Helena H\u00f6glander<\/figcaption><\/figure>\n\n\n\n

The biological carbon pump (BCP)<\/strong> is a suite of biologically mediated processes that transfer carbon fixed by photosynthesis in the sunlit surface ocean (euphotic zone) into the ocean interior, sequestering it away from exchange with the atmosphere on timescales of months to millennia.<\/p>\n\n\n\n

It is a major component of the global carbon cycle. Phytoplankton perform roughly half of Earth\u2019s photosynthesis, drawing down dissolved inorganic carbon<\/strong> (DIC, including CO\u2082) and helping the ocean absorb atmospheric CO\u2082<\/strong>. Without the BCP, atmospheric CO\u2082 would be substantially higher (estimates often cite ~200 ppm higher in a world without export).<\/p>\n\n\n\n

The BCP is often discussed alongside the solubility (or physical) pump and the carbonate (or alkalinity and hard- tissue) pump. A related concept is the microbial carbon pump, which transforms labile dissolved organic carbon (DOC)<\/strong> into more refractory forms that can persist for centuries to millennia.<\/p>\n\n\n\n

Core Stages of the Biological Carbon Pump<\/strong><\/h3>\n\n\n\n
    \n
  1. Primary production:<\/strong> Phytoplankton (including diatoms, coccolithophores, and picocyanobacteria such as Synechococcus<\/em>) fix CO\u2082 into organic matter (particulate organic carbon (POC) and dissolved organic carbon (DOC) via photosynthesis in the euphotic zone<\/strong>.<\/li>\n\n\n\n
  2. Food- web processing and transformation:<\/strong> Much of the fixed carbon is rapidly recycled in the surface layer by grazing, respiration, and bacterial degradation (the microbial loop). A fraction escapes recycling and is available for export.<\/li>\n\n\n\n
  3. Export from the surface:<\/strong> Organic carbon (and some inorganic carbon) moves downward via multiple pathways.<\/li>\n\n\n\n
  4. Attenuation and remineralization:<\/strong> As material sinks or is transported, microbes and zooplankton consume and respire it, releasing CO\u2082 (DIC) at various depths. The depth of remineralization largely determines how long the carbon is sequestered.<\/li>\n\n\n\n
  5. Sequestration:<\/strong> Carbon that reaches greater depths (or is transported into poorly ventilated water masses) remains isolated from the atmosphere longer.<\/li>\n<\/ol>\n\n\n\n

    Main Export Mechanisms (Pathways)<\/strong><\/h3>\n\n\n\n

    Modern frameworks often group processes into three broad categories (gravitational, migrant, and mixing\/physical injection pumps), sometimes expanded into six more specific \u201cparticle injection pumps\u201d<\/strong>.\u2060<\/a><\/p>\n\n\n\n

    1. Gravitational (sinking) pump:<\/strong> The classic pathway, often the largest contributor to net export.<\/p>\n\n\n\n