In a modest office on Geng Road in Palo Alto, a small team of scientists is attempting something that might sound more science fiction than startup: engineering seaweed to pull carbon dioxide from the atmosphere and lock it away for geological timescales. CarbonDrop—formerly CarbonLock before someone presumably decided that name was a bit too on the nose—has now attracted $19,624,984 in Series A funding to make that vision a reality.
The round closed in May with 18 investors, according to Securities and Exchange Commission filings amended on May 6. First capital trickled in as early as March 19, a detail that hints at the choreography involved in assembling this particular syndicate.
What started as a $16,424,985 commitment from 15 backers ultimately swelled to just over $19.6 million. The company raised the funds under Regulation D Rule 506(b)—an equity offering that, notably, reported no sales commissions or finder's fees. For context, CarbonDrop had previously secured $13.5 million in seed funding that wrapped in April 2023, bringing 11 investors to the table then.
Blue-chip believers
The investor roster reads like a who's who of West Coast venture capital, according to SEC filings. Benchmark, the storied Sand Hill Road firm, is in. So is Collaborative Fund, known for backing companies at the nexus of social impact and returns. SEC filings name Benchmark general partners Bruce W. Dunlevie and Peter Fenton as directors, with Dunlevie taking on the CEO role—a somewhat unusual arrangement that suggests hands-on involvement from the investment side. Craig Shapiro, founder and managing partner of Collaborative Fund, also holds a board seat. Rounding out the directors is Mike Farmwald, a serial entrepreneur whose previous ventures have ranged from memory technology to data infrastructure.
That's a lot of firepower for a company with somewhere between 2 and 10 employees, though headcounts at early-stage startups tend to be moving targets. (The range reflects data pulled in recent weeks and could have shifted since.)
The seaweed science
Founded in 2021, CarbonDrop develops what it calls molecular tools for engineering macroalgae—a fancy term for the large seaweeds that grow in coastal waters. The idea is to harness photosynthesis, that miraculous process by which plants turn sunlight and CO2 into energy, and supercharge it for carbon removal at scale. If successful, the captured carbon would be stored not for years but for what the company describes as "geologically-relevant timescales." Translate that: long enough to matter for the climate.
Vincent Boudreau, identified as a founding team member and director of scientific research, leads the seaweed engineering efforts. A May 2025 presentation from the Center for Cellular Construction offered a glimpse into the work, though details remain closely held. Arthur Grossman, a plant biologist with affiliations at both Stanford and the Carnegie Institution, lends his expertise in a scientific advisory role. It's the kind of academic pedigree that signals this isn't just another carbon credit arbitrage play.
A crowded, complicated field
Macroalgae-based carbon removal sits at a fascinating—and messy—intersection. It's part biological engineering, part ocean-based climate intervention, and entirely experimental at commercial scale. A May 2026 paper published in Frontiers in Climate laid out the current state of play, highlighting persistent methodology and monitoring challenges. How do you verify that carbon dumped into the ocean actually stays there? How do you measure it? These aren't trivial questions when buyers are paying for certified removal.
CarbonDrop isn't alone in chasing ocean-based solutions. Ebb Carbon, for instance, raised $20 million in April 2023—what was then the largest investment in ocean-based carbon removal technology—for its ocean alkalinity enhancement technology. Graphyte, which takes a different tack by storing biomass, pulled in $30 million in July 2024. Funding rounds in this emerging sector vary widely, reflecting both the diversity of approaches and the experimental nature of the field.
What's conspicuously absent from CarbonDrop's story so far? Customers. The company hasn't publicly announced any commercial offtake agreements or partnerships with carbon credit buyers. Its website remains sparse—no press section, no detailed technical disclosures beyond a LinkedIn description that's more teaser than reveal. Perhaps that's intentional, a sign that the science is still too nascent to sell. Or maybe the pitch is aimed squarely at the next funding round, not today's carbon markets.
Either way, Benchmark doesn't typically write checks—or install its partners as CEO—without a thesis. Whether seaweed can scale as a climate solution remains an open question. But with nearly $33 million in the bank and some of venture capital's sharpest minds involved, CarbonDrop has bought itself time to find out.
